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# Permutations

Permutations
You are encouraged to solve this task according to the task description, using any language you may know.

Write a program that generates all   permutations   of   n   different objects.   (Practically numerals!)

The number of samples of size k from n objects.

With   combinations and permutations   generation tasks.

Order Unimportant Order Important
Without replacement ${\displaystyle {\binom {n}{k}}=^{n}\operatorname {C} _{k}={\frac {n(n-1)\ldots (n-k+1)}{k(k-1)\dots 1}}}$ ${\displaystyle ^{n}\operatorname {P} _{k}=n\cdot (n-1)\cdot (n-2)\cdots (n-k+1)}$
With replacement ${\displaystyle {\binom {n+k-1}{k}}=^{n+k-1}\operatorname {C} _{k}={(n+k-1)! \over (n-1)!k!}}$ ${\displaystyle n^{k}}$

## 11l

V a = [1, 2, 3]
L
print(a)
I !a.next_permutation()
L.break
Output:
[1, 2, 3]
[1, 3, 2]
[2, 1, 3]
[2, 3, 1]
[3, 1, 2]
[3, 2, 1]

## 360 Assembly

Translation of: Liberty BASIC
*        Permutations              26/10/2015
PERMUTE CSECT
USING PERMUTE,R15 set base register
LA R9,TMP-A n=hbound(a)
SR R10,R10 nn=0
LOOP LA R10,1(R10) nn=nn+1
LA R11,PG [email protected]
LA R6,1 i=1
LOOPI1 CR R6,R9 do i=1 to n
BH ELOOPI1
LA R2,A-1(R6) @a(i)
MVC 0(1,R11),0(R2) output a(i)
LA R11,1(R11) pgi=pgi+1
LA R6,1(R6) i=i+1
B LOOPI1
ELOOPI1 XPRNT PG,80
LR R6,R9 i=n
LOOPUIM BCTR R6,0 i=i-1
LTR R6,R6 until i=0
BE ELOOPUIM
LA R2,A-1(R6) @a(i)
LA R3,A(R6) @a(i+1)
CLC 0(1,R2),0(R3) or until a(i)<a(i+1)
BNL LOOPUIM
ELOOPUIM LR R7,R6 j=i
LA R7,1(R7) j=i+1
LR R8,R9 k=n
LOOPWJ CR R7,R8 do while j<k
BNL ELOOPWJ
LA R2,A-1(R7) [email protected](j)
LA R3,A-1(R8) [email protected](k)
MVC TMP,0(R2) tmp=a(j)
MVC 0(1,R2),0(R3) a(j)=a(k)
MVC 0(1,R3),TMP a(k)=tmp
LA R7,1(R7) j=j+1
BCTR R8,0 k=k-1
B LOOPWJ
ELOOPWJ LTR R6,R6 if i>0
BNP ILE0
LR R7,R6 j=i
LA R7,1(R7) j=i+1
LOOPWA LA R2,A-1(R7) @a(j)
LA R3,A-1(R6) @a(i)
CLC 0(1,R2),0(R3) do while a(j)<a(i)
BNL AJGEAI
LA R7,1(R7) j=j+1
B LOOPWA
AJGEAI LA R2,A-1(R7) [email protected](j)
LA R3,A-1(R6) [email protected](i)
MVC TMP,0(R2) tmp=a(j)
MVC 0(1,R2),0(R3) a(j)=a(i)
MVC 0(1,R3),TMP a(i)=tmp
ILE0 LTR R6,R6 until i<>0
BNE LOOP
XR R15,R15 set return code
A DC C'ABCD' <== input
TMP DS C temp for swap
PG DC CL80' ' buffer
YREGS
END PERMUTE
Output:
ABCD
ABDC
ACBD
ACDB
BACD
BCDA
BDAC
BDCA
CABD
CBDA
CDAB
CDBA
DABC
DACB
DBAC
DBCA
DCAB
DCBA

## AArch64 Assembly

Works with: as version Raspberry Pi 3B version Buster 64 bits

/* ARM assembly AARCH64 Raspberry PI 3B */
/* program permutation64.s */

/*******************************************/
/* Constantes file */
/*******************************************/
/* for this file see task include a file in language AArch64 assembly */
.include "../includeConstantesARM64.inc"

/*********************************/
/* Initialized data */
/*********************************/
.data

sMessResult: .asciz "Value  : @\n"
sMessCounter: .asciz "Permutations = @ \n"
szCarriageReturn: .asciz "\n"

.align 4
.equ NBELEMENTS, (. - TableNumber) / 8
/*********************************/
/* UnInitialized data */
/*********************************/
.bss
sZoneConv: .skip 24
/*********************************/
/* code section */
/*********************************/
.text
.global main
main: //entry of program
mov x1,NBELEMENTS //number of élements
mov x10,0 //counter
bl heapIteratif
mov x0,x10 //display counter
bl conversion10S //décimal conversion
bl strInsertAtCharInc
bl affichageMess //display message

100: //standard end of the program
mov x0,0 //return code
mov x8,EXIT //request to exit program
svc 0 //perform the system call

/******************************************************************/
/* permutation by heap iteratif (wikipedia) */
/******************************************************************/
/* x0 contains the address of table */
/* x1 contains the eléments number */
heapIteratif:
stp x2,lr,[sp,-16]! // save registers
stp x3,x4,[sp,-16]! // save registers
stp x5,x6,[sp,-16]! // save registers
stp x7,fp,[sp,-16]! // save registers
tst x1,1 // odd ?
csel x2,x2,x1,ne // the stack must be a multiple of 16
lsl x7,x2,3 // 8 bytes by count
sub sp,sp,x7
mov fp,sp
mov x3,#0
mov x4,#0 // index
1: // init area counter
str x4,[fp,x3,lsl 3]
cmp x3,x1
blt 1b

bl displayTable
mov x3,#0 // index
2:
ldr x4,[fp,x3,lsl 3] // load count [i]
cmp x4,x3 // compare with i
bge 5f
tst x3,#1 // even ?
bne 3f
ldr x5,[x0] // yes load value A[0]
ldr x6,[x0,x3,lsl 3] // and swap with value A[i]
str x6,[x0]
str x5,[x0,x3,lsl 3]
b 4f
3:
ldr x5,[x0,x4,lsl 3] // load value A[count[i]]
ldr x6,[x0,x3,lsl 3] // and swap with value A[i]
str x6,[x0,x4,lsl 3]
str x5,[x0,x3,lsl 3]
4:
bl displayTable
add x4,x4,1 // increment count i
str x4,[fp,x3,lsl 3] // and store on stack
mov x3,0 // raz index
b 2b // and loop
5:
mov x4,0 // raz count [i]
str x4,[fp,x3,lsl 3]
cmp x3,x1 // end ?
blt 2b // no -> loop

100:
ldp x7,fp,[sp],16 // restaur 2 registers
ldp x5,x6,[sp],16 // restaur 2 registers
ldp x3,x4,[sp],16 // restaur 2 registers
ldp x2,lr,[sp],16 // restaur 2 registers
/******************************************************************/
/* Display table elements */
/******************************************************************/
/* x0 contains the address of table */
displayTable:
stp x1,lr,[sp,-16]! // save registers
stp x2,x3,[sp,-16]! // save registers
mov x3,#0
1: // loop display table
ldr x0,[x2,x3,lsl 3]
bl conversion10S // décimal conversion
bl strInsertAtCharInc
bl affichageMess // display message
cmp x3,NBELEMENTS - 1
ble 1b
bl affichageMess
mov x0,x2
100:
ldp x2,x3,[sp],16 // restaur 2 registers
ldp x1,lr,[sp],16 // restaur 2 registers
/********************************************************/
/* File Include fonctions */
/********************************************************/
/* for this file see task include a file in language AArch64 assembly */
.include "../includeARM64.inc"

Value  : +1
Value  : +2
Value  : +3

Value  : +2
Value  : +1
Value  : +3

Value  : +3
Value  : +1
Value  : +2

Value  : +1
Value  : +3
Value  : +2

Value  : +2
Value  : +3
Value  : +1

Value  : +3
Value  : +2
Value  : +1

Permutations =  +6

## ABAP

data: lv_flag type c,
lv_number type i,
lt_numbers type table of i.

append 1 to lt_numbers.
append 2 to lt_numbers.
append 3 to lt_numbers.

do.
perform permute using lt_numbers changing lv_flag.
if lv_flag = 'X'.
exit.
endif.
loop at lt_numbers into lv_number.
write (1) lv_number no-gap left-justified.
if sy-tabix <> '3'.
write ', '.
endif.
endloop.
skip.
enddo.

" Permutation function - this is used to permute:
" Can be used for an unbounded size set.
form permute using iv_set like lt_numbers
changing ev_last type c.
data: lv_len type i,
lv_first type i,
lv_third type i,
lv_count type i,
lv_temp type i,
lv_temp_2 type i,
lv_second type i,
lv_changed type c,
lv_perm type i.
describe table iv_set lines lv_len.

lv_perm = lv_len - 1.
lv_changed = ' '.
" Loop backwards through the table, attempting to find elements which
" can be permuted. If we find one, break out of the table and set the
" flag indicating a switch.
do.
if lv_perm <= 0.
exit.
endif.
read table iv_set index lv_perm into lv_first.
read table iv_set index lv_perm into lv_second.
subtract 1 from lv_perm.
if lv_first < lv_second.
lv_changed = 'X'.
exit.
endif.
subtract 1 from lv_perm.
enddo.

" Last permutation.
if lv_changed <> 'X'.
ev_last = 'X'.
exit.
endif.

" Swap tail decresing to get a tail increasing.
lv_count = lv_perm + 1.
do.
lv_first = lv_len + lv_perm - lv_count + 1.
if lv_count >= lv_first.
exit.
endif.

read table iv_set index lv_count into lv_temp.
read table iv_set index lv_first into lv_temp_2.
modify iv_set index lv_count from lv_temp_2.
modify iv_set index lv_first from lv_temp.
enddo.

lv_count = lv_len - 1.
do.
if lv_count <= lv_perm.
exit.
endif.

read table iv_set index lv_count into lv_first.
read table iv_set index lv_perm into lv_second.
read table iv_set index lv_len into lv_third.
if ( lv_first < lv_third ) and ( lv_first > lv_second ).
lv_len = lv_count.
endif.

subtract 1 from lv_count.
enddo.

read table iv_set index lv_perm into lv_temp.
read table iv_set index lv_len into lv_temp_2.
modify iv_set index lv_perm from lv_temp_2.
modify iv_set index lv_len from lv_temp.
endform.
Output:
1,  3,  2

2,  1,  3

2,  3,  1

3,  1,  2

3,  2,  1

## Action!

PROC PrintArray(BYTE ARRAY a BYTE len)
BYTE i

FOR i=0 TO len-1
DO
PrintB(a(i))
OD
Print(" ")
RETURN

BYTE FUNC NextPermutation(BYTE ARRAY a BYTE len)
BYTE i,j,k,tmp

i=len-1
WHILE i>0 AND a(i-1)>a(i)
DO
i==-1
OD

j=i
k=len-1
WHILE j<k
DO
tmp=a(j) a(j)=a(k) a(k)=tmp
j==+1 k==-1
OD

IF i=0 THEN
RETURN (0)
FI

j=i
WHILE a(j)<a(i-1)
DO
j==+1
OD
tmp=a(i-1) a(i-1)=a(j) a(j)=tmp
RETURN (1)

PROC Main()
DEFINE len="5"
BYTE ARRAY a(len)
BYTE RMARGIN=$53,oldRMARGIN BYTE i oldRMARGIN=RMARGIN RMARGIN=37 ;change right margin on the screen FOR i=0 TO len-1 DO a(i)=i OD DO PrintArray(a,len) UNTIL NextPermutation(a,len)=0 OD RMARGIN=oldRMARGIN ;restore right margin on the screen RETURN Output: 01234 01243 01324 01342 01423 01432 02134 02143 02314 02341 02413 02431 03124 03142 03214 03241 03412 03421 04123 04132 04213 04231 04312 04321 10234 10243 10324 10342 10423 10432 12034 12043 12304 12340 12403 12430 13024 13042 13204 13240 13402 13420 14023 14032 14203 14230 14302 14320 20134 20143 20314 20341 20413 20431 21034 21043 21304 21340 21403 21430 23014 23041 23104 23140 23401 23410 24013 24031 24103 24130 24301 24310 30124 30142 30214 30241 30412 30421 31024 31042 31204 31240 31402 31420 32014 32041 32104 32140 32401 32410 34012 34021 34102 34120 34201 34210 40123 40132 40213 40231 40312 40321 41023 41032 41203 41230 41302 41320 42013 42031 42103 42130 42301 42310 43012 43021 43102 43120 43201 43210 ## Ada We split the task into two parts: The first part is to represent permutations, to initialize them and to go from one permutation to another one, until the last one has been reached. This can be used elsewhere, e.g., for the Topswaps [[1]] task. The second part is to read the N from the command line, and to actually print all permutations over 1 .. N. ### The generic package Generic_Perm When given N, this package defines the Element and Permutation types and exports procedures to set a permutation P to the first one, and to change P into the next one: generic N: positive; package Generic_Perm is subtype Element is Positive range 1 .. N; type Permutation is array(Element) of Element; procedure Set_To_First(P: out Permutation; Is_Last: out Boolean); procedure Go_To_Next(P: in out Permutation; Is_Last: out Boolean); end Generic_Perm; Here is the implementation of the package: package body Generic_Perm is procedure Set_To_First(P: out Permutation; Is_Last: out Boolean) is begin for I in P'Range loop P (I) := I; end loop; Is_Last := P'Length = 1; -- if P has a single element, the fist permutation is the last one end Set_To_First; procedure Go_To_Next(P: in out Permutation; Is_Last: out Boolean) is procedure Swap (A, B : in out Integer) is C : Integer := A; begin A := B; B := C; end Swap; I, J, K : Element; begin -- find longest tail decreasing sequence -- after the loop, this sequence is I+1 .. n, -- and the ith element will be exchanged later -- with some element of the tail Is_Last := True; I := N - 1; loop if P (I) < P (I+1) then Is_Last := False; exit; end if; -- next instruction will raise an exception if I = 1, so -- exit now (this is the last permutation) exit when I = 1; I := I - 1; end loop; -- if all the elements of the permutation are in -- decreasing order, this is the last one if Is_Last then return; end if; -- sort the tail, i.e. reverse it, since it is in decreasing order J := I + 1; K := N; while J < K loop Swap (P (J), P (K)); J := J + 1; K := K - 1; end loop; -- find lowest element in the tail greater than the ith element J := N; while P (J) > P (I) loop J := J - 1; end loop; J := J + 1; -- exchange them -- this will give the next permutation in lexicographic order, -- since every element from ith to the last is minimum Swap (P (I), P (J)); end Go_To_Next; end Generic_Perm; ### The procedure Print_Perms with Ada.Text_IO, Ada.Command_Line, Generic_Perm; procedure Print_Perms is package CML renames Ada.Command_Line; package TIO renames Ada.Text_IO; begin declare package Perms is new Generic_Perm(Positive'Value(CML.Argument(1))); P : Perms.Permutation; Done : Boolean := False; procedure Print(P: Perms.Permutation) is begin for I in P'Range loop TIO.Put (Perms.Element'Image (P (I))); end loop; TIO.New_Line; end Print; begin Perms.Set_To_First(P, Done); loop Print(P); exit when Done; Perms.Go_To_Next(P, Done); end loop; end; exception when Constraint_Error => TIO.Put_Line ("*** Error: enter one numerical argument n with n >= 1"); end Print_Perms; Output: >./print_perms 3 1 2 3 1 3 2 2 1 3 2 3 1 3 1 2 3 2 1 3 2 1 ## Aime void f1(record r, ...) { if (~r) { for (text s in r) { r.delete(s); rcall(f1, -2, 0, -1, s); r[s] = 0; } } else { ocall(o_, -2, 1, -1, " ", ","); o_newline(); } } main(...) { record r; ocall(r_put, -2, 1, -1, r, 0); f1(r); 0; } Output: aime permutations -a Aaa Bb C Aaa, Bb, C, Aaa, C, Bb, Bb, Aaa, C, Bb, C, Aaa, C, Aaa, Bb, C, Bb, Aaa, ## ALGOL 68 Works with: ALGOL 68 version Revision 1 - one minor extension to language used - PRAGMA READ, similar to C's #include directive. Works with: ALGOL 68G version Any - tested with release algol68g-2.6. File: prelude_permutations.a68 # -*- coding: utf-8 -*- # COMMENT REQUIRED BY "prelude_permutations.a68" MODE PERMDATA = ~; PROVIDES: # PERMDATA*=~* # # perm*=~ list* # END COMMENT MODE PERMDATALIST = REF[]PERMDATA; MODE PERMDATALISTYIELD = PROC(PERMDATALIST)VOID; # Generate permutations of the input data list of data list # PROC perm gen permutations = (PERMDATALIST data list, PERMDATALISTYIELD yield)VOID: ( # Warning: this routine does not correctly handle duplicate elements # IF LWB data list = UPB data list THEN yield(data list) ELSE FOR elem FROM LWB data list TO UPB data list DO PERMDATA first = data list[elem]; data list[LWB data list+1:elem] := data list[:elem-1]; data list[LWB data list] := first; # FOR PERMDATALIST next data list IN # perm gen permutations(data list[LWB data list+1:] # ) DO #, ## (PERMDATALIST next)VOID:( yield(data list) # OD #)); data list[:elem-1] := data list[LWB data list+1:elem]; data list[elem] := first OD FI ); SKIP File: test_permutations.a68 #!/usr/bin/a68g --script # # -*- coding: utf-8 -*- # CO REQUIRED BY "prelude_permutations.a68" CO MODE PERMDATA = INT; #PROVIDES:# # PERM*=INT* # # perm *=int list *# PR READ "prelude_permutations.a68" PR; main:( FLEX[0]PERMDATA test case := (1, 22, 333, 44444); INT upb data list = UPB test case; FORMAT data fmt :=$g(0)$, data list fmt :=$"("n(upb data list-1)(f(data fmt)", ")f(data fmt)")"$; # FOR DATALIST permutation IN # perm gen permutations(test case#) DO (#, ## (PERMDATALIST permutation)VOID:( printf((data list fmt, permutation,$l)) # OD #)) ) Output: (1, 22, 333, 44444) (1, 22, 44444, 333) (1, 333, 22, 44444) (1, 333, 44444, 22) (1, 44444, 22, 333) (1, 44444, 333, 22) (22, 1, 333, 44444) (22, 1, 44444, 333) (22, 333, 1, 44444) (22, 333, 44444, 1) (22, 44444, 1, 333) (22, 44444, 333, 1) (333, 1, 22, 44444) (333, 1, 44444, 22) (333, 22, 1, 44444) (333, 22, 44444, 1) (333, 44444, 1, 22) (333, 44444, 22, 1) (44444, 1, 22, 333) (44444, 1, 333, 22) (44444, 22, 1, 333) (44444, 22, 333, 1) (44444, 333, 1, 22) (44444, 333, 22, 1) ## Amazing Hopper Translation of: AWK /* hopper-JAMBO - a flavour of Amazing Hopper! */ #include <jambo.h> Main leng=0 Void(lista) Set("la realidad","escapa","a los sentidos"), Apnd list(lista) Length(lista), Move to(leng) Toksep(" ") Printnl( lista ) Set(1) Gosub(Permutar) End-Return Subrutines Define( Permutar, pos ) If ( Sub(leng, pos) Isgeq(1) ) i=pos Loop if( Less( i, leng ) ) Plusone(pos), Gosub(Permutar) Set( pos ), Gosub(Rotate) Printnl( lista ) ++i Back Plusone(pos), Gosub(Permutar) Set( pos ), Gosub(Rotate) End If Return Define ( Rotate, pos ) c=0, [pos] Get(lista), Move to(c) [ Plusone(pos): leng ] Cget(lista) [ pos: Minusone(leng) ] Cput(lista) Set(c), [ leng ] Cput(lista) Return Output: la realidad escapa a los sentidos la realidad a los sentidos escapa escapa a los sentidos la realidad escapa la realidad a los sentidos a los sentidos la realidad escapa a los sentidos escapa la realidad ## APL For Dyalog APL(assumes index origin ⎕IO←1): ⍝ Builtin version, takes a vector: ⎕CY'dfns' perms←{↓⍵[pmat ≢⍵]} ⍝ pmat always gives lexicographically ordered permutations. ⍝ Recursive fast implementation, courtesy of dzaima from The APL Orchard: dpmat←{1=⍵:,⊂,0 ⋄ (⊃,/)¨(⍳⍵)⌽¨⊂(⊂(!⍵-1)⍴⍵-1),⍨∇⍵-1} perms2←{↓⍵[1+⍉↑dpmat ≢⍵]} perms 'cat' ┌───┬───┬───┬───┬───┬───┐ │cat│cta│act│atc│tca│tac│ └───┴───┴───┴───┴───┴───┘ perms2 'cat' ┌───┬───┬───┬───┬───┬───┐ │cta│atc│tac│tca│act│cat│ └───┴───┴───┴───┴───┴───┘ ## AppleScript ### Recursive Translation of: JavaScript (Functional ES6 version) Recursively, in terms of concatMap and delete: ----------------------- PERMUTATIONS ----------------------- -- permutations :: [a] -> [[a]] on permutations(xs) script go on |λ|(xs) script h on |λ|(x) script ts on |λ|(ys) {{x} & ys} end |λ| end script concatMap(ts, go's |λ|(|delete|(x, xs))) end |λ| end script if {} ≠ xs then concatMap(h, xs) else {{}} end if end |λ| end script go's |λ|(xs) end permutations --------------------------- TEST --------------------------- on run permutations({"aardvarks", "eat", "ants"}) end run -------------------- GENERIC FUNCTIONS --------------------- -- concatMap :: (a -> [b]) -> [a] -> [b] on concatMap(f, xs) set lst to {} set lng to length of xs tell mReturn(f) repeat with i from 1 to lng set lst to (lst & |λ|(contents of item i of xs, i, xs)) end repeat end tell return lst end concatMap -- delete :: a -> [a] -> [a] on |delete|(x, xs) if length of xs > 0 then set {h, t} to uncons(xs) if x = h then t else {h} & |delete|(x, t) end if else {} end if end |delete| -- Lift 2nd class handler function into 1st class script wrapper -- mReturn :: Handler -> Script on mReturn(f) if class of f is script then f else script property |λ| : f end script end if end mReturn -- uncons :: [a] -> Maybe (a, [a]) on uncons(xs) if length of xs > 0 then {item 1 of xs, rest of xs} else missing value end if end uncons Output: {{"aardvarks", "eat", "ants"}, {"aardvarks", "ants", "eat"}, {"eat", "aardvarks", "ants"}, {"eat", "ants", "aardvarks"}, {"ants", "aardvarks", "eat"}, {"ants", "eat", "aardvarks"}} Translation of: Pseudocode (Fast recursive Heap's algorithm) to DoPermutations(aList, n) --> Heaps's algorithm (Permutation by interchanging pairs) if n = 1 then tell (a reference to PermList) to copy aList to its end -- or: copy aList as text (for concatenated results) else repeat with i from 1 to n DoPermutations(aList, n - 1) if n mod 2 = 0 then -- n is even tell aList to set [item i, item n] to [item n, item i] -- swaps items i and n of aList else tell aList to set [item 1, item n] to [item n, item 1] -- swaps items 1 and n of aList end if end repeat end if return (a reference to PermList) as list end DoPermutations --> Example 1 (list of words) set [SourceList, PermList] to [{"Good", "Johnny", "Be"}, {}] DoPermutations(SourceList, SourceList's length) --> result (value of PermList) {{"Good", "Johnny", "Be"}, {"Johnny", "Good", "Be"}, {"Be", "Good", "Johnny"}, ¬ {"Good", "Be", "Johnny"}, {"Johnny", "Be", "Good"}, {"Be", "Johnny", "Good"}} --> Example 2 (characters with concatenated results) set [SourceList, PermList] to [{"X", "Y", "Z"}, {}] DoPermutations(SourceList, SourceList's length) --> result (value of PermList) {"XYZ", "YXZ", "ZXY", "XZY", "YZX", "ZYX"} --> Example 3 (Integers) set [SourceList, Permlist] to [{1, 2, 3}, {}] DoPermutations(SourceList, SourceList's length) --> result (value of Permlist) {{1, 2, 3}, {2, 1, 3}, {3, 1, 2}, {1, 3, 2}, {2, 3, 1}, {3, 2, 1}} --> Example 4 (Integers with concatenated results) set [SourceList, Permlist] to [{1, 2, 3}, {}] DoPermutations(SourceList, SourceList's length) --> result (value of Permlist) {"123", "213", "312", "132", "231", "321"} ### Non-recursive As a right fold (which turns out to be significantly faster than recurse + delete): ----------------------- PERMUTATIONS ----------------------- -- permutations :: [a] -> [[a]] on permutations(xs) script go on |λ|(x, a) script on |λ|(ys) script infix on |λ|(n) if ys ≠ {} then take(n, ys) & {x} & drop(n, ys) else {x} end if end |λ| end script map(infix, enumFromTo(0, (length of ys))) end |λ| end script concatMap(result, a) end |λ| end script foldr(go, {{}}, xs) end permutations --------------------------- TEST --------------------------- on run permutations({1, 2, 3}) --> {{1, 2, 3}, {2, 1, 3}, {2, 3, 1}, {1, 3, 2}, {3, 1, 2}, {3, 2, 1}} end run ------------------------- GENERIC -------------------------- -- concatMap :: (a -> [b]) -> [a] -> [b] on concatMap(f, xs) set lng to length of xs set acc to {} tell mReturn(f) repeat with i from 1 to lng set acc to acc & |λ|(item i of xs, i, xs) end repeat end tell return acc end concatMap -- drop :: Int -> [a] -> [a] on drop(n, xs) if n < length of xs then items (1 + n) thru -1 of xs else {} end if end drop -- enumFromTo :: Int -> Int -> [Int] on enumFromTo(m, n) if m ≤ n then set lst to {} repeat with i from m to n set end of lst to i end repeat return lst else return {} end if end enumFromTo -- foldr :: (a -> b -> b) -> b -> [a] -> b on foldr(f, startValue, xs) tell mReturn(f) set v to startValue set lng to length of xs repeat with i from lng to 1 by -1 set v to |λ|(item i of xs, v, i, xs) end repeat return v end tell end foldr -- Lift 2nd class handler function into 1st class script wrapper -- mReturn :: First-class m => (a -> b) -> m (a -> b) on mReturn(f) if class of f is script then f else script property |λ| : f end script end if end mReturn -- map :: (a -> b) -> [a] -> [b] on map(f, xs) tell mReturn(f) set lng to length of xs set lst to {} repeat with i from 1 to lng set end of lst to |λ|(item i of xs, i, xs) end repeat return lst end tell end map -- min :: Ord a => a -> a -> a on min(x, y) if y < x then y else x end if end min -- take :: Int -> [a] -> [a] -- take :: Int -> String -> String on take(n, xs) if 0 < n then items 1 thru min(n, length of xs) of xs else {} end if end take Output: {{1, 2, 3}, {2, 1, 3}, {2, 3, 1}, {1, 3, 2}, {3, 1, 2}, {3, 2, 1}} ### Recursive again This is marginally faster even than the Pseudocode translation above and doesn't demarcate lists with square brackets, which don't officially exist in AppleScript. It now features tail call elimination and a rethink of way the results list is built which, on my machine, reduces the time taken to return the 362,880 permutations of a 9-item list from a minute to a second and a half. It'll even return the 3,628,800 permutations of a 10-item list without seizing up, in about 17 seconds. But make sure Script Editor doesn't attempt to display such large results or you'll need to force-quit it! -- AppleScript interpretation of "Improved version of Heap's method (recursive)" -- found in Robert Sedgewick's PDF document "Permutation Generation Methods" -- <https://www.cs.princeton.edu/~rs/talks/perms.pdf> -- Adapted to permute from right to left instead of vice versa and to eliminate tail calls. on allPermutations(theList) script o property workList : missing value property permutations : {} property r : (count theList) -- The work list's rightmost … property |r-1| : r - 1 -- … penultimate … property |r-2| : r - 2 -- … and penpenultimate indices. property p : 1 -- Index for the permutations list. -- Recursive handler. Stores copies of workList after permuting items l thru r. on prmt(l) set evenCount to ((r - l) mod 2 = 1) -- Permuting an even number of the work list's items? -- Tail call elimination repeat. Stops with the three rightmost items still to be permuted. repeat until (l = |r-2|) -- Recursively permute items (l + 1) thru r. set |l+1| to l + 1 prmt(|l+1|) -- And again after successive swaps of item l with others to its right. if (evenCount) then -- Permuting an even number of items. Swap item l with items from slots r to l + 1 in turn. repeat with swapIndex from r to |l+1| + 1 by -1 tell item l of my workList set item l of my workList to item swapIndex of my workList set item swapIndex of my workList to it end tell prmt(|l+1|) end repeat set swapIndex to |l+1| else -- Permuting an odd number of items. Always swap item l with item r. repeat (r - |l+1|) times tell item l of my workList set item l of my workList to item r of my workList set item r of my workList to it end tell prmt(|l+1|) end repeat set swapIndex to r end if -- Do the last swap with the current l, then reset to repeat in lieu of a tail recursion. tell item l of my workList set item l of my workList to item swapIndex of my workList set item swapIndex of my workList to it end tell set l to |l+1| set evenCount to (not evenCount) end repeat -- Store the current state of the work list. copy workList to item p of my permutations -- And five more times with permutations of the rightmost three items. -- (Written out here to save doing five more recursion branches.) set {v1, v2, v3} to items |r-2| thru r of my workList set item |r-1| of my workList to v3 set item r of my workList to v2 copy workList to item (p + 1) of my permutations set item |r-2| of my workList to v2 set item r of my workList to v1 copy workList to item (p + 2) of my permutations set item |r-1| of my workList to v1 set item r of my workList to v3 copy workList to item (p + 3) of my permutations set item |r-2| of my workList to v3 set item r of my workList to v2 copy workList to item (p + 4) of my permutations set item |r-1| of my workList to v2 set item r of my workList to v1 copy workList to item (p + 5) of my permutations set p to p + 6 end prmt end script if (o's r < 3) then -- Special-case fewer than three items. copy theList to the beginning of o's permutations if (o's r is 2) then set the end of o's permutations to theList's reverse else -- Otherwise set up to use the recursive handler. copy theList to o's workList -- "Growing" a long results list by appending each permutation to it -- takes a disproportionately long time. Instead, build a list of the -- appropriate factorial length beforehand, using concatenation. set o's permutations to {missing value, missing value} repeat with i from 3 to (count theList) set temp to o's permutations repeat (i - 1) times set o's permutations to o's permutations & temp end repeat end repeat o's prmt(1) end if return o's permutations end allPermutations return allPermutations({1, 2, "cat", "dog"}) Output: {{1, 2, "cat", "dog"}, {1, 2, "dog", "cat"}, {1, "cat", "dog", 2}, {1, "cat", 2, "dog"}, {1, "dog", 2, "cat"}, {1, "dog", "cat", 2}, {2, "dog", "cat", 1}, {2, "dog", 1, "cat"}, {2, "cat", 1, "dog"}, {2, "cat", "dog", 1}, {2, 1, "dog", "cat"}, {2, 1, "cat", "dog"}, {"cat", 1, 2, "dog"}, {"cat", 1, "dog", 2}, {"cat", 2, "dog", 1}, {"cat", 2, 1, "dog"}, {"cat", "dog", 1, 2}, {"cat", "dog", 2, 1}, {"dog", "cat", 2, 1}, {"dog", "cat", 1, 2}, {"dog", 2, 1, "cat"}, {"dog", 2, "cat", 1}, {"dog", 1, "cat", 2}, {"dog", 1, 2, "cat"}} ## ARM Assembly Works with: as version Raspberry Pi /* ARM assembly Raspberry PI */ /* program permutation.s */ /* REMARK 1 : this program use routines in a include file see task Include a file language arm assembly for the routine affichageMess conversion10 see at end of this program the instruction include */ /* for constantes see task include a file in arm assembly */ /************************************/ /* Constantes */ /************************************/ .include "../constantes.inc" /*********************************/ /* Initialized data */ /*********************************/ .data sMessResult: .asciz "Value : @ \n" sMessCounter: .asciz "Permutations = @ \n" szCarriageReturn: .asciz "\n" .align 4 TableNumber: .int 1,2,3 .equ NBELEMENTS, (. - TableNumber) / 4 /*********************************/ /* UnInitialized data */ /*********************************/ .bss sZoneConv: .skip 24 /*********************************/ /* code section */ /*********************************/ .text .global main main: @ entry of program ldr r0,iAdrTableNumber @ address number table mov r1,#NBELEMENTS @ number of élements mov r10,#0 @ counter bl heapIteratif mov r0,r10 @ display counter ldr r1,iAdrsZoneConv @ bl conversion10S @ décimal conversion ldr r0,iAdrsMessCounter ldr r1,iAdrsZoneConv @ insert conversion bl strInsertAtCharInc bl affichageMess @ display message 100: @ standard end of the program mov r0, #0 @ return code mov r7, #EXIT @ request to exit program svc #0 @ perform the system call iAdrszCarriageReturn: .int szCarriageReturn iAdrsMessResult: .int sMessResult iAdrTableNumber: .int TableNumber iAdrsMessCounter: .int sMessCounter /******************************************************************/ /* permutation by heap iteratif (wikipedia) */ /******************************************************************/ /* r0 contains the address of table */ /* r1 contains the eléments number */ heapIteratif: push {r3-r9,lr} @ save registers lsl r9,r1,#2 @ four bytes by count sub sp,sp,r9 mov fp,sp mov r3,#0 mov r4,#0 @ index 1: @ init area counter str r4,[fp,r3,lsl #2] add r3,r3,#1 cmp r3,r1 blt 1b bl displayTable add r10,r10,#1 mov r3,#0 @ index 2: ldr r4,[fp,r3,lsl #2] @ load count [i] cmp r4,r3 @ compare with i bge 5f tst r3,#1 @ even ? bne 3f ldr r5,[r0] @ yes load value A[0] ldr r6,[r0,r3,lsl #2] @ and swap with value A[i] str r6,[r0] str r5,[r0,r3,lsl #2] b 4f 3: ldr r5,[r0,r4,lsl #2] @ load value A[count[i]] ldr r6,[r0,r3,lsl #2] @ and swap with value A[i] str r6,[r0,r4,lsl #2] str r5,[r0,r3,lsl #2] 4: bl displayTable add r10,r10,#1 add r4,r4,#1 @ increment count i str r4,[fp,r3,lsl #2] @ and store on stack mov r3,#0 @ raz index b 2b @ and loop 5: mov r4,#0 @ raz count [i] str r4,[fp,r3,lsl #2] add r3,r3,#1 @ increment index cmp r3,r1 @ end ? blt 2b @ no -> loop add sp,sp,r9 @ stack alignement 100: pop {r3-r9,lr} bx lr @ return /******************************************************************/ /* Display table elements */ /******************************************************************/ /* r0 contains the address of table */ displayTable: push {r0-r3,lr} @ save registers mov r2,r0 @ table address mov r3,#0 1: @ loop display table ldr r0,[r2,r3,lsl #2] ldr r1,iAdrsZoneConv @ bl conversion10S @ décimal conversion ldr r0,iAdrsMessResult ldr r1,iAdrsZoneConv @ insert conversion bl strInsertAtCharInc bl affichageMess @ display message add r3,#1 cmp r3,#NBELEMENTS - 1 ble 1b ldr r0,iAdrszCarriageReturn bl affichageMess mov r0,r2 100: pop {r0-r3,lr} bx lr iAdrsZoneConv: .int sZoneConv /***************************************************/ /* ROUTINES INCLUDE */ /***************************************************/ .include "../affichage.inc" Value : +1 Value : +2 Value : +3 Value : +2 Value : +1 Value : +3 Value : +3 Value : +1 Value : +2 Value : +1 Value : +3 Value : +2 Value : +2 Value : +3 Value : +1 Value : +3 Value : +2 Value : +1 Permutations = +6 ## Arturo print permutate [1 2 3] Output: [1 2 3] [1 3 2] [3 1 2] [2 1 3] [2 3 1] [3 2 1] ## AutoHotkey from the forum topic http://www.autohotkey.com/forum/viewtopic.php?t=77959 #NoEnv StringCaseSense On o := str := "Hello" Loop { str := perm_next(str) If !str { MsgBox % clipboard := o break } o.= "n" . str } perm_Next(str){ p := 0, sLen := StrLen(str) Loop % sLen { If A_Index=1 continue t := SubStr(str, sLen+1-A_Index, 1) n := SubStr(str, sLen+2-A_Index, 1) If ( t < n ) { p := sLen+1-A_Index, pC := SubStr(str, p, 1) break } } If !p return false Loop { t := SubStr(str, sLen+1-A_Index, 1) If ( t > pC ) { n := sLen+1-A_Index, nC := SubStr(str, n, 1) break } } return SubStr(str, 1, p-1) . nC . Reverse(SubStr(str, p+1, n-p-1) . pC . SubStr(str, n+1)) } Reverse(s){ Loop Parse, s o := A_LoopField o return o } Output: Hello Helol Heoll Hlelo Hleol Hlleo Hlloe Hloel Hlole Hoell Holel Holle eHllo eHlol eHoll elHlo elHol ellHo elloH eloHl elolH eoHll eolHl eollH lHelo lHeol lHleo lHloe lHoel lHole leHlo leHol lelHo leloH leoHl leolH llHeo llHoe lleHo lleoH lloHe lloeH loHel loHle loeHl loelH lolHe loleH oHell oHlel oHlle oeHll oelHl oellH olHel olHle oleHl olelH ollHe olleH ### Alternate Version Alternate version to produce numerical permutations of combinations. P(n,k="",opt=0,delim="",str="") { ; generate all n choose k permutations lexicographically ;1..n = range, or delimited list, or string to parse ; to process with a different min index, pass a delimited list, e.g. "0n1n2" ;k = length of result ;opt 0 = no repetitions ;opt 1 = with repetitions ;opt 2 = run for 1..k ;opt 3 = run for 1..k with repetitions ;str = string to prepend (used internally) ;returns delimited string, error message, or (if k > n) a blank string i:=0 If !InStr(n,"n") If n in 2,3,4,5,6,7,8,9 Loop, %n% n := A_Index = 1 ? A_Index : n "n" A_Index Else Loop, Parse, n, %delim% n := A_Index = 1 ? A_LoopField : n "n" A_LoopField If (k = "") RegExReplace(n,"n","",k), k++ If k is not Digit Return "k must be a digit." If opt not in 0,1,2,3 Return "opt invalid." If k = 0 Return str Else Loop, Parse, n, n If (!InStr(str,A_LoopField) || opt & 1) s .= (!i++ ? (opt & 2 ? str "n" : "") : "n" ) . P(n,k-1,opt,delim,str . A_LoopField . delim) Return s } Output: MsgBox % P(3) --------------------------- permute.ahk --------------------------- 123 132 213 231 312 321 --------------------------- OK --------------------------- MsgBox % P("Hello",3) --------------------------- permute.ahk --------------------------- Hel Hel Heo Hle Hlo Hle Hlo Hoe Hol Hol eHl eHl eHo elH elo elH elo eoH eol eol lHe lHo leH leo loH loe lHe lHo leH leo loH loe oHe oHl oHl oeH oel oel olH ole olH ole --------------------------- OK --------------------------- MsgBox % P("2n3n4n5",2,3) --------------------------- permute.ahk --------------------------- 2 22 23 24 25 3 32 33 34 35 4 42 43 44 45 5 52 53 54 55 --------------------------- OK --------------------------- MsgBox % P("11 a text ] u+z",3,0," ") --------------------------- permute.ahk --------------------------- 11 a text 11 a ] 11 a u+z 11 text a 11 text ] 11 text u+z 11 ] a 11 ] text 11 ] u+z 11 u+z a 11 u+z text 11 u+z ] a 11 text a 11 ] a 11 u+z a text 11 a text ] a text u+z a ] 11 a ] text a ] u+z a u+z 11 a u+z text a u+z ] text 11 a text 11 ] text 11 u+z text a 11 text a ] text a u+z text ] 11 text ] a text ] u+z text u+z 11 text u+z a text u+z ] ] 11 a ] 11 text ] 11 u+z ] a 11 ] a text ] a u+z ] text 11 ] text a ] text u+z ] u+z 11 ] u+z a ] u+z text u+z 11 a u+z 11 text u+z 11 ] u+z a 11 u+z a text u+z a ] u+z text 11 u+z text a u+z text ] u+z ] 11 u+z ] a u+z ] text --------------------------- OK --------------------------- ## AWK # syntax: GAWK -f PERMUTATIONS.AWK [-v sep=x] [word] # # examples: # REM all permutations on one line # GAWK -f PERMUTATIONS.AWK # # REM all permutations on a separate line # GAWK -f PERMUTATIONS.AWK -v sep="\n" # # REM use a different word # GAWK -f PERMUTATIONS.AWK Gwen # # REM command used for RosettaCode output # GAWK -f PERMUTATIONS.AWK -v sep="\n" Gwen # BEGIN { sep = (sep == "") ? " " : substr(sep,1,1) str = (ARGC == 1) ? "abc" : ARGV[1] printf("%s%s",str,sep) leng = length(str) for (i=1; i<=leng; i++) { arr[i-1] = substr(str,i,1) } ana_permute(0) exit(0) } function ana_permute(pos, i,j,str) { if (leng - pos < 2) { return } for (i=pos; i<leng-1; i++) { ana_permute(pos+1) ana_rotate(pos) for (j=0; j<=leng-1; j++) { printf("%s",arr[j]) } printf(sep) } ana_permute(pos+1) ana_rotate(pos) } function ana_rotate(pos, c,i) { c = arr[pos] for (i=pos; i<leng-1; i++) { arr[i] = arr[i+1] } arr[leng-1] = c } sample command: GAWK -f PERMUTATIONS.AWK Gwen Output: Gwen Gwne Genw Gewn Gnwe Gnew wenG weGn wnGe wneG wGen wGne enGw enwG eGwn eGnw ewnG ewGn nGwe nGew nweG nwGe neGw newG ## BASIC256 Translation of: Liberty BASIC arraybase 1 n = 4 : cont = 0 dim a(n) dim c(n) for j = 1 to n a[j] = j next j do for i = 1 to n print a[i]; next print " "; i = n cont += 1 if cont = 12 then print cont = 0 else print " "; end if do i -= 1 until (i = 0) or (a[i] < a[i+1]) j = i + 1 k = n while j < k tmp = a[j] : a[j] = a[k] : a[k] = tmp j += 1 k -= 1 end while if i > 0 then j = i + 1 while a[j] < a[i] j += 1 end while tmp = a[j] : a[j] = a[i] : a[i] = tmp end if until i = 0 end ## Batch File Recursive permutation generator. @echo off setlocal enabledelayedexpansion set arr=ABCD set /a n=4 :: echo !arr! call :permu %n% arr goto:eof :permu num &arr setlocal if %1 equ 1 call echo(!%2! & exit /b set /a "num=%1-1,n2=num-1" set arr=!%2! for /L %%c in (0,1,!n2!) do ( call:permu !num! arr set /a n1="num&1" if !n1! equ 0 (call:swapit !num! 0 arr) else (call:swapit !num! %%c arr) ) call:permu !num! arr endlocal & set %2=%arr% exit /b :swapit from to &arr setlocal set arr=!%3! set temp1=!arr:~%~1,1! set temp2=!arr:~%~2,1! set arr=!arr:%temp1%[email protected]! set arr=!arr:%temp2%=%temp1%! set arr=!arr:@=%temp2%! :: echo %1 %2 !%~3! !arr! endlocal & set %3=%arr% exit /b Output: ABCD BACD CABD ACBD BCAD CBAD DBAC BDAC ADBC DABC BADC ABDC ACDB CADB DACB ADCB CDAB DCAB DCBA CDBA BDCA DBCA CBDA BCDA ## BBC BASIC The procedure PROC_NextPermutation() will give the next lexicographic permutation of an integer array. DIM List%(3) List%() = 1, 2, 3, 4 FOR perm% = 1 TO 24 FOR i% = 0 TO DIM(List%(),1) PRINT List%(i%); NEXT PRINT PROC_NextPermutation(List%()) NEXT END DEF PROC_NextPermutation(A%()) LOCAL first, last, elementcount, pos elementcount = DIM(A%(),1) IF elementcount < 1 THEN ENDPROC pos = elementcount-1 WHILE A%(pos) >= A%(pos+1) pos -= 1 IF pos < 0 THEN PROC_Permutation_Reverse(A%(), 0, elementcount) ENDPROC ENDIF ENDWHILE last = elementcount WHILE A%(last) <= A%(pos) last -= 1 ENDWHILE SWAP A%(pos), A%(last) PROC_Permutation_Reverse(A%(), pos+1, elementcount) ENDPROC DEF PROC_Permutation_Reverse(A%(), first, last) WHILE first < last SWAP A%(first), A%(last) first += 1 last -= 1 ENDWHILE ENDPROC Output: 1 2 3 4 1 2 4 3 1 3 2 4 1 3 4 2 1 4 2 3 1 4 3 2 2 1 3 4 2 1 4 3 2 3 1 4 2 3 4 1 2 4 1 3 2 4 3 1 3 1 2 4 3 1 4 2 3 2 1 4 3 2 4 1 3 4 1 2 3 4 2 1 4 1 2 3 4 1 3 2 4 2 1 3 4 2 3 1 4 3 1 2 4 3 2 1 ## Bracmat ( perm = prefix List result original A Z . !arg:(?.) | !arg:(?prefix.?List:?original) & :?result & whl ' ( !List:%?A ?Z & !result perm(!prefix !A.!Z):?result
& !Z !A:~!original:?List
)
& !result
)
& out$(perm$(.a 2 "]" u+z);

Output:

(a 2 ] u+z.)
(a 2 u+z ].)
(a ] u+z 2.)
(a ] 2 u+z.)
(a u+z 2 ].)
(a u+z ] 2.)
(2 ] u+z a.)
(2 ] a u+z.)
(2 u+z a ].)
(2 u+z ] a.)
(2 a ] u+z.)
(2 a u+z ].)
(] u+z a 2.)
(] u+z 2 a.)
(] a 2 u+z.)
(] a u+z 2.)
(] 2 u+z a.)
(] 2 a u+z.)
(u+z a 2 ].)
(u+z a ] 2.)
(u+z 2 ] a.)
(u+z 2 a ].)
(u+z ] a 2.)
(u+z ] 2 a.)

## C

### version 1

Non-recursive algorithm to generate all permutations. It prints objects in lexicographical order.

#include <stdio.h>
int main (int argc, char *argv[]) {
//here we check arguments
if (argc < 2) {
printf("Enter an argument. Example 1234 or dcba:\n");
return 0;
}
//it calculates an array's length
int x;
for (x = 0; argv[1][x] != '\0'; x++);
//buble sort the array
int f, v, m;
for(f=0; f < x; f++) {
for(v = x-1; v > f; v-- ) {
if (argv[1][v-1] > argv[1][v]) {
m=argv[1][v-1];
argv[1][v-1]=argv[1][v];
argv[1][v]=m;
}
}
}

//it calculates a factorial to stop the algorithm
char a[x];
int k=0;
int fact=k+1;
while (k!=x) {
a[k]=argv[1][k];
k++;
fact = k*fact;
}
a[k]='\0';
//Main part: here we permutate
int i, j;
int y=0;
char c;
while (y != fact) {
printf("%s\n", a);
i=x-2;
while(a[i] > a[i+1] ) i--;
j=x-1;
while(a[j] < a[i] ) j--;
c=a[j];
a[j]=a[i];
a[i]=c;
i++;
for (j = x-1; j > i; i++, j--) {
c = a[i];
a[i] = a[j];
a[j] = c;
}
y++;
}
}

### version 2

Non-recursive algorithm to generate all permutations. It prints them from right to left.

#include <stdio.h>
int main() {
char a[] = "4321"; //array
int i, j;
int f=24; //factorial
char c; //buffer
while (f--) {
printf("%s\n", a);
i=1;
while(a[i] > a[i-1]) i++;
j=0;
while(a[j] < a[i])j++;
c=a[j];
a[j]=a[i];
a[i]=c;
i--;
for (j = 0; j < i; i--, j++) {
c = a[i];
a[i] = a[j];
a[j] = c;
}
}
}

### version 3

See lexicographic generation of permutations.

#include <stdio.h>
#include <stdlib.h>

/* print a list of ints */
int show(int *x, int len)
{
int i;
for (i = 0; i < len; i++)
printf("%d%c", x[i], i == len - 1 ? '\n' : ' ');
return 1;
}

/* next lexicographical permutation */
int next_lex_perm(int *a, int n) {
# define swap(i, j) {t = a[i]; a[i] = a[j]; a[j] = t;}
int k, l, t;

/* 1. Find the largest index k such that a[k] < a[k + 1]. If no such
index exists, the permutation is the last permutation. */

for (k = n - 1; k && a[k - 1] >= a[k]; k--);
if (!k--) return 0;

/* 2. Find the largest index l such that a[k] < a[l]. Since k + 1 is
such an index, l is well defined */

for (l = n - 1; a[l] <= a[k]; l--);

/* 3. Swap a[k] with a[l] */
swap(k, l);

/* 4. Reverse the sequence from a[k + 1] to the end */
for (k++, l = n - 1; l > k; l--, k++)
swap(k, l);
return 1;
# undef swap
}

void perm1(int *x, int n, int callback(int *, int))
{
do {
if (callback) callback(x, n);
} while (next_lex_perm(x, n));
}

/* Boothroyd method; exactly N! swaps, about as fast as it gets */
void boothroyd(int *x, int n, int nn, int callback(int *, int))
{
int c = 0, i, t;
while (1) {
if (n > 2) boothroyd(x, n - 1, nn, callback);
if (c >= n - 1) return;

i = (n & 1) ? 0 : c;
c++;
t = x[n - 1], x[n - 1] = x[i], x[i] = t;
if (callback) callback(x, nn);
}
}

/* entry for Boothroyd method */
void perm2(int *x, int n, int callback(int*, int))
{
if (callback) callback(x, n);
boothroyd(x, n, n, callback);
}

/* same as perm2, but flattened recursions into iterations */
void perm3(int *x, int n, int callback(int*, int))
{
/* calloc isn't strictly necessary, int c[32] would suffice
for most practical purposes */

int d, i, t, *c = calloc(n, sizeof(int));

/* curiously, with GCC 4.6.1 -O3, removing next line makes
it ~25% slower */

if (callback) callback(x, n);
for (d = 1; ; c[d]++) {
while (d > 1) c[--d] = 0;
while (c[d] >= d)
if (++d >= n) goto done;

t = x[ i = (d & 1) ? c[d] : 0 ], x[i] = x[d], x[d] = t;
if (callback) callback(x, n);
}
done: free(c);
}

#define N 4

int main()
{
int i, x[N];
for (i = 0; i < N; i++) x[i] = i + 1;

/* three different methods */
perm1(x, N, show);
perm2(x, N, show);
perm3(x, N, show);

return 0;
}

### version 4

See lexicographic generation of permutations.

#include <stdio.h>
#include <stdlib.h>

/* print a list of ints */
int show(int *x, int len)
{
int i;
for (i = 0; i < len; i++)
printf("%d%c", x[i], i == len - 1 ? '\n' : ' ');
return 1;
}

/* next lexicographical permutation */
int next_lex_perm(int *a, int n) {
# define swap(i, j) {t = a[i]; a[i] = a[j]; a[j] = t;}
int k, l, t;

/* 1. Find the largest index k such that a[k] < a[k + 1]. If no such
index exists, the permutation is the last permutation. */

for (k = n - 1; k && a[k - 1] >= a[k]; k--);
if (!k--) return 0;

/* 2. Find the largest index l such that a[k] < a[l]. Since k + 1 is
such an index, l is well defined */

for (l = n - 1; a[l] <= a[k]; l--);

/* 3. Swap a[k] with a[l] */
swap(k, l);

/* 4. Reverse the sequence from a[k + 1] to the end */
for (k++, l = n - 1; l > k; l--, k++)
swap(k, l);
return 1;
# undef swap
}

void perm1(int *x, int n, int callback(int *, int))
{
do {
if (callback) callback(x, n);
} while (next_lex_perm(x, n));
}

/* Boothroyd method; exactly N! swaps, about as fast as it gets */
void boothroyd(int *x, int n, int nn, int callback(int *, int))
{
int c = 0, i, t;
while (1) {
if (n > 2) boothroyd(x, n - 1, nn, callback);
if (c >= n - 1) return;

i = (n & 1) ? 0 : c;
c++;
t = x[n - 1], x[n - 1] = x[i], x[i] = t;
if (callback) callback(x, nn);
}
}

/* entry for Boothroyd method */
void perm2(int *x, int n, int callback(int*, int))
{
if (callback) callback(x, n);
boothroyd(x, n, n, callback);
}

/* same as perm2, but flattened recursions into iterations */
void perm3(int *x, int n, int callback(int*, int))
{
/* calloc isn't strictly necessary, int c[32] would suffice
for most practical purposes */

int d, i, t, *c = calloc(n, sizeof(int));

/* curiously, with GCC 4.6.1 -O3, removing next line makes
it ~25% slower */

if (callback) callback(x, n);
for (d = 1; ; c[d]++) {
while (d > 1) c[--d] = 0;
while (c[d] >= d)
if (++d >= n) goto done;

t = x[ i = (d & 1) ? c[d] : 0 ], x[i] = x[d], x[d] = t;
if (callback) callback(x, n);
}
done: free(c);
}

#define N 4

int main()
{
int i, x[N];
for (i = 0; i < N; i++) x[i] = i + 1;

/* three different methods */
perm1(x, N, show);
perm2(x, N, show);
perm3(x, N, show);

return 0;
}

## C#

Recursive Linq

Works with: C# version 7
public static class Extension
{
public static IEnumerable<IEnumerable<T>> Permutations<T>(this IEnumerable<T> values) where T : IComparable<T>
{
if (values.Count() == 1)
return new[] { values };
return values.SelectMany(v => Permutations(values.Where(x => x.CompareTo(v) != 0)), (v, p) => p.Prepend(v));
}
}

Usage

Enumerable.Range(0,5).Permutations()

A recursive Iterator. Runs under C#2 (VS2005), i.e. no var, no lambdas,...

public class Permutations<T>
{
public static System.Collections.Generic.IEnumerable<T[]> AllFor(T[] array)
{
if (array == null || array.Length == 0)
{
yield return new T[0];
}
else
{
for (int pick = 0; pick < array.Length; ++pick)
{
T item = array[pick];
int i = -1;
T[] rest = System.Array.FindAll<T>(
array, delegate(T p) { return ++i != pick; }
);
foreach (T[] restPermuted in AllFor(rest))
{
i = -1;
yield return System.Array.ConvertAll<T, T>(
array,
delegate(T p) {
return ++i == 0 ? item : restPermuted[i - 1];
}
);
}
}
}
}
}

Usage:

namespace Permutations_On_RosettaCode
{
class Program
{
static void Main(string[] args)
{
string[] list = "a b c d".Split();
foreach (string[] permutation in Permutations<string>.AllFor(list))
{
System.Console.WriteLine(string.Join(" ", permutation));
}
}
}
}

Recursive version

using System;
class Permutations
{
static int n = 4;
static int [] buf = new int [n];
static bool [] used = new bool [n];

static void Main()
{
for (int i = 0; i < n; i++) used [i] = false;
rec(0);
}

static void rec(int ind)
{
for (int i = 0; i < n; i++)
{
if (!used [i])
{
used [i] = true;
buf [ind] = i;
if (ind + 1 < n) rec(ind + 1);
else Console.WriteLine(string.Join(",", buf));
used [i] = false;
}
}
}
}

Alternate recursive version

using System;
class Permutations
{
static int n = 4;
static int [] buf = new int [n];
static int [] next = new int [n+1];

static void Main()
{
for (int i = 0; i < n; i++) next [i] = i + 1;
next[n] = 0;
rec(0);
}

static void rec(int ind)
{
for (int i = n; next[i] != n; i = next[i])
{
buf [ind] = next[i];
next[i]=next[next[i]];
if (ind < n - 1) rec(ind + 1);
else Console.WriteLine(string.Join(",", buf));
next[i] = buf [ind];
}
}
}

## C++

The C++ standard library provides for this in the form of std::next_permutation and std::prev_permutation.

#include <algorithm>
#include <string>
#include <vector>
#include <iostream>

template<class T>
void print(const std::vector<T> &vec)
{
for (typename std::vector<T>::const_iterator i = vec.begin(); i != vec.end(); ++i)
{
std::cout << *i;
if ((i + 1) != vec.end())
std::cout << ",";
}
std::cout << std::endl;
}

int main()
{
//Permutations for strings
std::string example("Hello");
std::sort(example.begin(), example.end());
do {
std::cout << example << '\n';
} while (std::next_permutation(example.begin(), example.end()));

// And for vectors
std::vector<int> another;
another.push_back(1234);
another.push_back(4321);
another.push_back(1234);
another.push_back(9999);

std::sort(another.begin(), another.end());
do {
print(another);
} while (std::next_permutation(another.begin(), another.end()));

return 0;
}
Output:
Hello
Helol
Heoll
Hlelo
Hleol
Hlleo
Hlloe
Hloel
Hlole
Hoell
Holel
Holle
eHllo
eHlol
eHoll
elHlo
elHol
ellHo
elloH
eloHl
elolH
eoHll
eolHl
eollH
lHelo
lHeol
lHleo
lHloe
lHoel
lHole
leHlo
leHol
lelHo
leloH
leoHl
leolH
llHeo
llHoe
lleHo
lleoH
lloHe
lloeH
loHel
loHle
loeHl
loelH
lolHe
loleH
oHell
oHlel
oHlle
oeHll
oelHl
oellH
olHel
olHle
oleHl
olelH
ollHe
olleH
1234,1234,4321,9999
1234,1234,9999,4321
1234,4321,1234,9999
1234,4321,9999,1234
1234,9999,1234,4321
1234,9999,4321,1234
4321,1234,1234,9999
4321,1234,9999,1234
4321,9999,1234,1234
9999,1234,1234,4321
9999,1234,4321,1234
9999,4321,1234,1234

## Clojure

### Library function

In an REPL:

user=> (require 'clojure.contrib.combinatorics)
nil
user=> (clojure.contrib.combinatorics/permutations [1 2 3])
((1 2 3) (1 3 2) (2 1 3) (2 3 1) (3 1 2) (3 2 1))

### Explicit

Replacing the call to the combinatorics library function by its real implementation.

(defn- iter-perm [v]
(let [len (count v),
j (loop [i (- len 2)]
(cond (= i -1) nil
(< (v i) (v (inc i))) i
:else (recur (dec i))))]
(when j
(let [vj (v j),
l (loop [i (dec len)]
(if (< vj (v i)) i (recur (dec i))))]
(loop [v (assoc v j (v l) l vj), k (inc j), l (dec len)]
(if (< k l)
(recur (assoc v k (v l) l (v k)) (inc k) (dec l))
v))))))

(defn- vec-lex-permutations [v]
(when v (cons v (lazy-seq (vec-lex-permutations (iter-perm v))))))

(defn lex-permutations
"Fast lexicographic permutation generator for a sequence of numbers"
[c]
(lazy-seq
(let [vec-sorted (vec (sort c))]
(if (zero? (count vec-sorted))
(list [])
(vec-lex-permutations vec-sorted)))))

(defn permutations
"All the permutations of items, lexicographic by index"
[items]
(let [v (vec items)]
(map #(map v %) (lex-permutations (range (count v))))))

(println (permutations [1 2 3]))

## CoffeeScript

# Returns a copy of an array with the element at a specific position
# removed from it.
arrayExcept = (arr, idx) ->
res = arr[0..]
res.splice idx, 1
res

# The actual function which returns the permutations of an array-like
# object (or a proper array).
permute = (arr) ->
arr = Array::slice.call arr, 0
return [[]] if arr.length == 0

permutations = (for value,idx in arr
[value].concat perm for perm in permute arrayExcept arr, idx)

# Flatten the array before returning it.
[].concat permutations...

This implementation utilises the fact that the permutations of an array could be defined recursively, with the fixed point being the permutations of an empty array.

Usage:
coffee> console.log (permute "123").join "\n"
1,2,3
1,3,2
2,1,3
2,3,1
3,1,2
3,2,1

## Common Lisp

(defun permute (list)
(if list
(mapcan #'(lambda (x)
(mapcar #'(lambda (y) (cons x y))
(permute (remove x list))))
list)
'(()))) ; else

(print (permute '(A B Z)))
Output:
((A B Z) (A Z B) (B A Z) (B Z A) (Z A B) (Z B A))

Lexicographic next permutation:

(defun next-perm (vec cmp)  ; modify vector
(declare (type (simple-array * (*)) vec))
(macrolet ((el (i) (aref vec ,i))
(cmp (i j) (funcall cmp (el ,i) (el ,j))))
(loop with len = (1- (length vec))
for i from (1- len) downto 0
when (cmp i (1+ i)) do
(loop for k from len downto i
when (cmp i k) do
(rotatef (el i) (el k))
(setf k (1+ len))
(loop while (< (incf i) (decf k)) do
(rotatef (el i) (el k)))
(return-from next-perm vec)))))

;;; test code
(loop for a = "1234" then (next-perm a #'char<) while a do
(write-line a))

Recursive implementation of Heap's algorithm:

(defun heap-permutations (seq)
(let ((permutations nil))
(labels ((permute (seq k)
(if (= k 1)
(push seq permutations)
(progn
(permute seq (1- k))
(loop for i from 0 below (1- k) do
(if (evenp k)
(rotatef (elt seq i) (elt seq (1- k)))
(rotatef (elt seq 0) (elt seq (1- k))))
(permute seq (1- k)))))))
(permute seq (length seq))
permutations)))

## Crystal

puts [1, 2, 3].permutations
Output:
[[1, 2, 3], [1, 3, 2], [2, 1, 3], [2, 3, 1], [3, 1, 2], [3, 2, 1]]

## Curry

insert :: a -> [a] -> [a]
insert x xs = x : xs
insert x (y:ys) = y : insert x ys

permutation :: [a] -> [a]
permutation [] = []
permutation (x:xs) = insert x $permutation xs ## D ### Simple Eager version Compile with -version=permutations1_main to see the output. T[][] permutations(T)(T[] items) pure nothrow { T[][] result; void perms(T[] s, T[] prefix=[]) nothrow { if (s.length) foreach (immutable i, immutable c; s) perms(s[0 .. i] ~ s[i+1 ..$], prefix ~ c);
else
result ~= prefix;
}

perms(items);
return result;
}

version (permutations1_main) {
void main() {
import std.stdio;
writefln("%(%s\n%)", [1, 2, 3].permutations);
}
}
Output:
[1, 2, 3]
[1, 3, 2]
[2, 1, 3]
[2, 3, 1]
[3, 1, 2]
[3, 2, 1]

### Fast Lazy Version

Compiled with -version=permutations2_main produces its output.

import std.algorithm, std.conv, std.traits;

struct Permutations(bool doCopy=true, T) if (isMutable!T) {
private immutable size_t num;
private T[] items;
private uint[31] indexes;
private ulong tot;

this (T[] items) pure nothrow @safe @nogc
in {
static enum string L = indexes.length.text;
assert(items.length >= 0 && items.length <= indexes.length,
"Permutations: items.length must be >= 0 && < " ~ L);
} body {
static ulong factorial(in size_t n) pure nothrow @safe @nogc {
ulong result = 1;
foreach (immutable i; 2 .. n + 1)
result *= i;
return result;
}

this.num = items.length;
this.items = items;
foreach (immutable i; 0 .. cast(typeof(indexes[0]))this.num)
this.indexes[i] = i;
this.tot = factorial(this.num);
}

@property T[] front() pure nothrow @safe {
static if (doCopy) {
return items.dup;
} else
return items;
}

@property bool empty() const pure nothrow @safe @nogc {
}

@property size_t length() const pure nothrow @safe @nogc {
// Not cached to keep the function pure.
typeof(return) result = 1;
foreach (immutable x; 1 .. items.length + 1)
result *= x;
return result;
}

void popFront() pure nothrow @safe @nogc {
tot--;
if (tot > 0) {
size_t j = num - 2;

while (indexes[j] > indexes[j + 1])
j--;
size_t k = num - 1;
while (indexes[j] > indexes[k])
k--;
swap(indexes[k], indexes[j]);
swap(items[k], items[j]);

size_t r = num - 1;
size_t s = j + 1;
while (r > s) {
swap(indexes[s], indexes[r]);
swap(items[s], items[r]);
r--;
s++;
}
}
}
}

Permutations!(doCopy,T) permutations(bool doCopy=true, T)
(T[] items)
pure nothrow if (isMutable!T) {
return Permutations!(doCopy, T)(items);
}

version (permutations2_main) {
void main() {
import std.stdio, std.bigint;
alias B = BigInt;
foreach (p; [B(1), B(2), B(3)].permutations)
assert((p[0] + 1) > 0);
[1, 2, 3].permutations!false.writeln;
[B(1), B(2), B(3)].permutations!false.writeln;
}
}

### Standard Version

void main() {
import std.stdio, std.algorithm;

auto items = [1, 2, 3];
do
items.writeln;
while (items.nextPermutation);
}

## Delphi

program TestPermutations;

{$APPTYPE CONSOLE} type TItem = Integer; // declare ordinal type for array item TArray = array[0..3] of TItem; const Source: TArray = (1, 2, 3, 4); procedure Permutation(K: Integer; var A: TArray); var I, J: Integer; Tmp: TItem; begin for I:= Low(A) + 1 to High(A) + 1 do begin J:= K mod I; Tmp:= A[J]; A[J]:= A[I - 1]; A[I - 1]:= Tmp; K:= K div I; end; end; var A: TArray; I, K, Count: Integer; S, S1, S2: ShortString; begin Count:= 1; I:= Length(A); while I > 1 do begin Count:= Count * I; Dec(I); end; S:= ''; for K:= 0 to Count - 1 do begin A:= Source; Permutation(K, A); S1:= ''; for I:= Low(A) to High(A) do begin Str(A[I]:1, S2); S1:= S1 + S2; end; S:= S + ' ' + S1; if Length(S) > 40 then begin Writeln(S); S:= ''; end; end; if Length(S) > 0 then Writeln(S); Readln; end. Output: 4123 4213 4312 4321 4132 4231 3421 3412 2413 1423 2431 1432 3142 3241 2341 1342 2143 1243 3124 3214 2314 1324 2134 1234 ## EDSAC order code Uses two subroutines which respectively (1) Generate the first permutation in lexicographic order; (2) Return the next permutation in lexicographic order, or set a flag to indicate there are no more permutations. The algorithm for (2) is the same as in the Wikipedia article "Permutation". [Permutations task for Rosetta Code.] [EDSAC program, Initial Orders 2.] T51K P200F [G parameter: start address of subroutines] T47K P100F [M parameter: start address of main routine] [====================== G parameter: Subroutines =====================] E25K TG GK [Constants used in the subroutines] [0] AF [add to address to make A order for that address] [1] SF [add to address to make S order for that address] [2] UF [(1) add to address to make U order for that address] [(2) subtract from S order to make T order, same address] [3] OF [add to A order to make T order, same address] [----------------------------------------------------------- Subroutine to initialize an array of n short (17-bit) words to 0, 1, 2, ..., n-1 (in the address field). Parameters: 4F = address of array; 5F = n = length of array. Workspace: 0F, 1F.] [4] A3F [plant return link as usual] [email protected] A4F [address of array] [email protected] [make U order for that address] T1F [store U order in 1F] A5F [load n = number of elements (in address field)] S2F [make n-1] [Start of loop; works backwards, n-1 to 0] [11] UF [store array element in 0F] A1F [make order to store element in array] [email protected] [plant that order in code] AF [pick up element fron 0F] [15] UF [(planted) store element in array] S2F [dec to next element] [email protected] [loop if still >= 0] TF [clear acc. before return] [19] ZF [overwritten by jump back to caller] [------------------------------------------------------------------- Subroutine to get next permutation in lexicographic order. Uses same 4-step algorithm as Wikipedia article "Permutations", but notation in comments differs from that in Wikipedia. Parameters: 4F = address of array; 5F = n = length of array. 0F is returned as 0 for success, < 0 if passed-in permutation is the last. Workspace: 0F, 1F.] [20] A3F [plant return link as usual] [email protected] [Step 1: Find the largest index k such that a{k} > a{k-1}. If no such index exists, the passed-in permutation is the last.] A4F [load address of a{0}] [email protected] [make A order for a{0}] U1F [store as test for end of loop] A5F [make A order for a{n}] [email protected] [plant in code below] S2F [make A order for a{n-1}] [email protected] [plant in code below] A4F [load address of a{0}] A5F [make address of a{n}] [email protected] [make S order for a{n}] [email protected] [plant in code below] [Start of loop for comparing a{k} with a{k-1}] [33] TF [clear acc] [email protected] [load A order for a{k}] S2F [make A order for a{k-1}] S1F [tested all yet?] [email protected] [if yes, jump to failed (no more permutations)] A1F [restore accumulator after test] [email protected] [plant updated A order] [email protected] [dec address in S order] S2F [email protected] [43] SF [(planted) load a{k-1}] [44] AF [(planted) subtract a{k}] [email protected] [loop back if a{k-1} > a{k}] [Step 2: Find the largest index j >= k such that a{j} > a{k-1}. Such an index j exists, because j = k is an instance.] TF [clear acc] A4F [load address of a{0}] A5F [make address of a{n}] [email protected] [make S order for a{n}] T1F [save as test for end of loop] [email protected] [load S order for a{k}] [email protected] [plant in code below] [email protected] [load A order for a{k-1}] [email protected] [plant in code below] [Start of loop] [55] TF [clear acc] [email protected] [load S order for a{j} (initially j = k)] [email protected] [plant in code below] A2F [inc address (in effect inc j)] S1F [test for end of array] [email protected] [jump out if so] A1F [restore acc after test] [email protected] [update S order] [63] AF [(planted) load a{k-1}] [64] SF [(planted) subtract a{j}] [email protected] [loop back if a{j} still > a{k-1}] [66] [Step 3: Swap a{k-1} and a{j}] TF [clear acc] [email protected] [load A order for a{k-1}] [email protected] [plant in code below, 2 places] [email protected] [email protected] [make T order for a{k-1}] [email protected] [plant in code below] [email protected] [load S order for a{j}] [email protected] [make T order for a{j}] [email protected] [plant in code below] [75] SF [(planted) load -a{j}] TF [park -a{j} in 0F] [77] AF [(planted) load a{k-1}] [78] TF [(planted) store a{j}] SF [load a{j} by subtracting -a{j}] [80] TF [(planted) store in a{k-1}] [Step 4: Now a{k}, ..., a{n-1} are in decreasing order. Change to increasing order by repeated swapping.] [81] [email protected] [counting down from a{n} (exclusive end of array)] S2F [make A order for a{n-1}] [email protected] [plant in code] [email protected] [make T order for a{n-1}] [email protected] [plant] [email protected] [counting up from a{k-1} (exclusive)] A2F [make A order for a{k}] [email protected] [plant] [email protected] [make T order for a{k}] [email protected] [plant] [email protected] [swapped all yet?] [email protected] [if yes, jump to exit from subroutine] [Swapping two array elements, initially a{k} and a{n-1}] TF [clear acc] [94] AF [(planted) load 1st element] TF [park in 0F] [96] AF [(planted) load 2nd element] [97] TF [(planted) copy to 1st element] AF [load old 1st element] [99] TF [(planted) copy to 2nd element] [email protected] [always loop back] [101] TF [done, return 0 in location 0F] [102] TF [return status to caller in 0F; also clears acc] [103] ZF [(planted) jump back to caller] [==================== M parameter: Main routine ==================] [Prints all 120 permutations of the letters in 'EDSAC'.] E25K TM GK [Constants used in the main routine] [0] P900F [address of permutation array] [1] P5F [number of elements in permutation (in address field)] [Array of letters in 'EDSAC', in alphabetical order] [2] AF CF DF EF SF [7] [email protected] [add to index to make O order for letter in array] [8] P12F [permutations per printed line (in address field)] [9] AF [add to address to make A order for that address] [Teleprinter characters] [10] K2048F [set letters mode] [11] !F [space] [12] @F [carriage return] [13] &F [line feed] [14] K4096F [null] [Entry point, with acc = 0.] [15] [email protected] [set teleprinter to letters] [email protected] [intialize -ve count of permutations per line] T7F [keep count in 7F] [email protected] [pass address of permutation array in 4F] T4F [email protected] [pass number of elements in 5F] T5F [22] [email protected] [call subroutine to initialize permutation array] G4G [Loop: print current permutation, then get next (if any)] [24] A4F [address] [email protected] [make A order] [email protected] [plant in code] S5F [initialize -ve count of array elements] [28] T6F [keep count in 6F] [29] AF [(planted) load permutation element] [email protected] [make order to print letter from table] [email protected] [plant in code] [32] OF [(planted) print letter from table] [email protected] [inc address in permutation array] A2F [email protected] A6F [inc -ve count of array elements] A2F [email protected] [loop till count becomes 0] A7F [inc -ve count of perms per line] A2F [email protected] [jump if end of line] [email protected] [else print a space] [email protected] [join common code] [44] [email protected] [print CR] [email protected] [print LF] [email protected] [47] T7F [update -ve count of permutations in line] [48] [email protected] [call subroutine for next permutation (if any)] G20G AF [test 0F: got a new permutation?] [email protected] [if so, loop to print it] [email protected] [no more, output null to flush teleprinter buffer] ZF [halt program] E15Z [define entry point] PF [enter with acc = 0] [end] Output: ACDES ACDSE ACEDS ACESD ACSDE ACSED ADCES ADCSE ADECS ADESC ADSCE ADSEC AECDS AECSD AEDCS AEDSC AESCD AESDC ASCDE ASCED ASDCE ASDEC ASECD ASEDC CADES CADSE CAEDS CAESD CASDE CASED CDAES CDASE CDEAS CDESA CDSAE CDSEA CEADS CEASD CEDAS CEDSA CESAD CESDA CSADE CSAED CSDAE CSDEA CSEAD CSEDA DACES DACSE DAECS DAESC DASCE DASEC DCAES DCASE DCEAS DCESA DCSAE DCSEA DEACS DEASC DECAS DECSA DESAC DESCA DSACE DSAEC DSCAE DSCEA DSEAC DSECA EACDS EACSD EADCS EADSC EASCD EASDC ECADS ECASD ECDAS ECDSA ECSAD ECSDA EDACS EDASC EDCAS EDCSA EDSAC EDSCA ESACD ESADC ESCAD ESCDA ESDAC ESDCA SACDE SACED SADCE SADEC SAECD SAEDC SCADE SCAED SCDAE SCDEA SCEAD SCEDA SDACE SDAEC SDCAE SDCEA SDEAC SDECA SEACD SEADC SECAD SECDA SEDAC SEDCA ## Eiffel class APPLICATION create make feature {NONE} make do test := <<2, 5, 1>> permute (test, 1) end test: ARRAY [INTEGER] permute (a: ARRAY [INTEGER]; k: INTEGER) -- All permutations of 'a'. require count_positive: a.count > 0 k_valid_index: k > 0 local t: INTEGER do if k = a.count then across a as ar loop io.put_integer (ar.item) end io.new_line else across k |..| a.count as c loop t := a [k] a [k] := a [c.item] a [c.item] := t permute (a, k + 1) t := a [k] a [k] := a [c.item] a [c.item] := t end end end end Output: 251 215 521 512 152 125 ## Elixir Translation of: Erlang defmodule RC do def permute([]), do: [[]] def permute(list) do for x <- list, y <- permute(list -- [x]), do: [x|y] end end IO.inspect RC.permute([1, 2, 3]) Output: [[1, 2, 3], [1, 3, 2], [2, 1, 3], [2, 3, 1], [3, 1, 2], [3, 2, 1]] ## Erlang Shortest form: -module(permute). -export([permute/1]). permute([]) -> [[]]; permute(L) -> [[X|Y] || X<-L, Y<-permute(L--[X])]. Y-combinator (for shell): F = fun(L) -> G = fun(_, []) -> [[]]; (F, L) -> [[X|Y] || X<-L, Y<-F(F, L--[X])] end, G(G, L) end. More efficient zipper implementation: -module(permute). -export([permute/1]). permute([]) -> [[]]; permute(L) -> zipper(L, [], []). % Use zipper to pick up first element of permutation zipper([], _, Acc) -> lists:reverse(Acc); zipper([H|T], R, Acc) -> % place current member in front of all permutations % of rest of set - both sides of zipper prepend(H, permute(lists:reverse(R, T)), % pass zipper state for continuation T, [H|R], Acc). prepend(_, [], T, R, Acc) -> zipper(T, R, Acc); % continue in zipper prepend(X, [H|T], ZT, ZR, Acc) -> prepend(X, T, ZT, ZR, [[X|H]|Acc]). Demonstration (escript): main(_) -> io:fwrite("~p~n", [permute:permute([1,2,3])]). Output: [[1,2,3],[1,3,2],[2,1,3],[2,3,1],[3,1,2],[3,2,1]] ## Euphoria Translation of: PureBasic function reverse(sequence s, integer first, integer last) object x while first < last do x = s[first] s[first] = s[last] s[last] = x first += 1 last -= 1 end while return s end function function nextPermutation(sequence s) integer pos, last object x if length(s) < 1 then return 0 end if pos = length(s)-1 while compare(s[pos], s[pos+1]) >= 0 do pos -= 1 if pos < 1 then return -1 end if end while last = length(s) while compare(s[last], s[pos]) <= 0 do last -= 1 end while x = s[pos] s[pos] = s[last] s[last] = x return reverse(s, pos+1, length(s)) end function object s s = "abcd" puts(1, s & '\t') while 1 do s = nextPermutation(s) if atom(s) then exit end if puts(1, s & '\t') end while Output: abcd abdc acbd acdb adbc adcb bacd badc bcad bcda bdac bdca cabd cadb cbad cbda cdab cdba dabc dacb dbac dbca dcab dcba ## F# let rec insert left x right = seq { match right with | [] -> yield left @ [x] | head :: tail -> yield left @ [x] @ right yield! insert (left @ [head]) x tail } let rec perms permute = seq { match permute with | [] -> yield [] | head :: tail -> yield! Seq.collect (insert [] head) (perms tail) } [<EntryPoint>] let main argv = perms (Seq.toList argv) |> Seq.iter (fun x -> printf "%A\n" x) 0 >RosettaPermutations 1 2 3 ["1"; "2"; "3"] ["2"; "1"; "3"] ["2"; "3"; "1"] ["1"; "3"; "2"] ["3"; "1"; "2"] ["3"; "2"; "1"] Translation of Haskell "insertion-based approach" (last version) let permutations xs = let rec insert x = function | [] -> [[x]] | head :: tail -> (x :: (head :: tail)) :: (List.map (fun l -> head :: l) (insert x tail)) List.fold (fun s e -> List.collect (insert e) s) [[]] xs ## Factor The all-permutations word is part of factor's standard library. See http://docs.factorcode.org/content/word-all-permutations,math.combinatorics.html ## Fortran program permutations implicit none integer, parameter :: value_min = 1 integer, parameter :: value_max = 3 integer, parameter :: position_min = value_min integer, parameter :: position_max = value_max integer, dimension (position_min : position_max) :: permutation call generate (position_min) contains recursive subroutine generate (position) implicit none integer, intent (in) :: position integer :: value if (position > position_max) then write (*, *) permutation else do value = value_min, value_max if (.not. any (permutation (: position - 1) == value)) then permutation (position) = value call generate (position + 1) end if end do end if end subroutine generate end program permutations Output: 1 2 3 1 3 2 2 1 3 2 3 1 3 1 2 3 2 1 ### Alternate solution Instead of looking up unused values, this program starts from [1, ..., n] and does only swaps, hence the array always represents a valid permutation. The values need to be "swapped back" after the recursive call. program allperm implicit none integer :: n, i integer, allocatable :: a(:) read *, n allocate(a(n)) a = [ (i, i = 1, n) ] call perm(1) deallocate(a) contains recursive subroutine perm(i) integer :: i, j, t if (i == n) then print *, a else do j = i, n t = a(i) a(i) = a(j) a(j) = t call perm(i + 1) t = a(i) a(i) = a(j) a(j) = t end do end if end subroutine end program ### Fortran Speed Test So ... what is the fastest algorithm? Here below is the speed test for a couple of algorithms of permutation. We can add more algorithms into this frame-work. When they work in the same circumstance, we can see which is the fastest one. program testing_permutation_algorithms implicit none integer :: nmax integer, dimension(:),allocatable :: ida logical :: mtc logical :: even integer :: i integer(8) :: ic integer :: clock_rate, clock_max, t1, t2 real(8) :: dt integer :: pos_min, pos_max ! ! ! Beginning: ! write(*,*) 'INPUT N:' read *, nmax write(*,*) 'N =', nmax allocate ( ida(1:nmax) ) ! ! ! (1) Starting: ! do i = 1, nmax ida(i) = i enddo ! ic = 0 call system_clock ( t1, clock_rate, clock_max ) ! mtc = .false. ! do call subnexper ( nmax, ida, mtc, even ) ! ! 1) counting the number of permutatations ! ic = ic + 1 ! ! 2) writing out the result: ! ! do i = 1, nmax ! write (100,"(i3,',')",advance = "no") ida(i) ! enddo ! write(100,*) ! ! repeat if not being finished yet, otherwise exit. ! if (mtc) then cycle else exit endif ! enddo ! call system_clock ( t2, clock_rate, clock_max ) dt = ( dble(t2) - dble(t1) )/ dble(clock_rate) ! ! Finishing (1) ! write(*,*) "1) subnexper:" write(*,*) 'Total permutations :', ic write(*,*) 'Total time elapsed :', dt ! ! ! (2) Starting: ! do i = 1, nmax ida(i) = i enddo ! pos_min = 1 pos_max = nmax ! ic = 0 call system_clock ( t1, clock_rate, clock_max ) ! call generate ( pos_min ) ! call system_clock ( t2, clock_rate, clock_max ) dt = ( dble(t2) - dble(t1) )/ dble(clock_rate) ! ! Finishing (2) ! write(*,*) "2) generate:" write(*,*) 'Total permutations :', ic write(*,*) 'Total time elapsed :', dt ! ! ! (3) Starting: ! do i = 1, nmax ida(i) = i enddo ! ic = 0 call system_clock ( t1, clock_rate, clock_max ) ! i = 1 call perm ( i ) ! call system_clock ( t2, clock_rate, clock_max ) dt = ( dble(t2) - dble(t1) )/ dble(clock_rate) ! ! Finishing (3) ! write(*,*) "3) perm:" write(*,*) 'Total permutations :', ic write(*,*) 'Total time elapsed :', dt ! ! ! (4) Starting: ! do i = 1, nmax ida(i) = i enddo ! ic = 0 call system_clock ( t1, clock_rate, clock_max ) ! do ! ! 1) counting the number of permutatations ! ic = ic + 1 ! ! 2) writing out the result: ! ! do i = 1, nmax ! write (100,"(i3,',')",advance = "no") ida(i) ! enddo ! write(100,*) ! ! repeat if not being finished yet, otherwise exit. ! if ( nextp(nmax,ida) ) then cycle else exit endif ! enddo ! call system_clock ( t2, clock_rate, clock_max ) dt = ( dble(t2) - dble(t1) )/ dble(clock_rate) ! ! Finishing (4) ! write(*,*) "4) nextp:" write(*,*) 'Total permutations :', ic write(*,*) 'Total time elapsed :', dt ! ! ! What's else? ! ... ! !== deallocate(ida) ! stop !== contains !== ! Modified version of SUBROUTINE NEXPER from the book of ! Albert Nijenhuis and Herbert S. Wilf, "Combinatorial ! Algorithms For Computers and Calculators", 2nd Ed, p.59. ! subroutine subnexper ( n, a, mtc, even ) implicit none integer,intent(in) :: n integer,dimension(n),intent(inout) :: a logical,intent(inout) :: mtc, even ! ! local varialbes: ! integer,save :: nm3 integer :: ia, i, s, d, i1, l, j, m ! if (mtc) goto 10 nm3 = n-3 do i = 1,n a(i) = i enddo mtc = .true. 5 even = .true. if ( n .eq. 1 ) goto 8 6 if ( a(n) .ne. 1 .or. a(1) .ne. 2+mod(n,2) ) return if ( n .le. 3 ) goto 8 do i = 1,nm3 if( a(i+1) .ne. a(i)+1 ) return enddo 8 mtc = .false. return 10 if ( n .eq. 1 ) goto 27 if( .not. even ) goto 20 ia = a(1) a(1) = a(2) a(2) = ia even = .false. goto 6 20 s = 0 do i1 = 2,n ia = a(i1) i = i1-1 d = 0 do j = 1,i if ( a(j) .gt. ia ) d = d+1 enddo s = d+s if ( d .ne. i*mod(s,2) ) goto 35 enddo 27 a(1) = 0 goto 8 35 m = mod(s+1,2)*(n+1) do j = 1,i if(isign(1,a(j)-ia) .eq. isign(1,a(j)-m)) cycle m = a(j) l = j enddo a(l) = ia a(i1) = m even = .true. return end subroutine !===== ! ! http://rosettacode.org/wiki/Permutations#Fortran ! recursive subroutine generate (pos) implicit none integer,intent(in) :: pos integer :: val if (pos > pos_max) then ! ! 1) counting the number of permutatations ! ic = ic + 1 ! ! 2) writing out the result: ! ! write (*,*) permutation ! else do val = 1, nmax if (.not. any (ida( : pos-1) == val)) then ida(pos) = val call generate (pos + 1) endif enddo endif end subroutine !===== ! ! http://rosettacode.org/wiki/Permutations#Fortran ! recursive subroutine perm (i) implicit none integer,intent(inout) :: i ! integer :: j, t, ip1 ! if (i == nmax) then ! ! 1) couting the number of permutatations ! ic = ic + 1 ! ! 2) writing out the result: ! ! write (*,*) a ! else ip1 = i+1 do j = i, nmax t = ida(i) ida(i) = ida(j) ida(j) = t call perm ( ip1 ) t = ida(i) ida(i) = ida(j) ida(j) = t enddo endif return end subroutine !===== ! ! http://rosettacode.org/wiki/Permutations#Fortran ! function nextp ( n, a ) logical :: nextp integer,intent(in) :: n integer,dimension(n),intent(inout) :: a ! ! local variables: ! integer i,j,k,t ! i = n-1 10 if ( a(i) .lt. a(i+1) ) goto 20 i = i-1 if ( i .eq. 0 ) goto 20 goto 10 20 j = i+1 k = n 30 t = a(j) a(j) = a(k) a(k) = t j = j+1 k = k-1 if ( j .lt. k ) goto 30 j = i if (j .ne. 0 ) goto 40 ! nextp = .false. ! return ! 40 j = j+1 if ( a(j) .lt. a(i) ) goto 40 t = a(i) a(i) = a(j) a(j) = t ! nextp = .true. ! return end function !===== ! ! What's else ? ! ... !===== end program An example of performance: 1) Compiled with GNU fortran compiler: gfortran -O3 testing_permutation_algorithms.f90 ; ./a.out INPUT N: 10 N = 10 1) subnexper: Total permutations : 3628800 Total time elapsed : 4.9000000000000002E-002 2) generate: Total permutations : 3628800 Total time elapsed : 0.84299999999999997 3) perm: Total permutations : 3628800 Total time elapsed : 5.6000000000000001E-002 4) nextp: Total permutations : 3628800 Total time elapsed : 2.9999999999999999E-002 b) Compiled with Intel compiler: ifort -O3 testing_permutation_algorithms.f90 ; ./a.out INPUT N: 10 N = 10 1) subnexper: Total permutations : 3628800 Total time elapsed : 8.240000000000000E-002 2) generate: Total permutations : 3628800 Total time elapsed : 0.616200000000000 3) perm: Total permutations : 3628800 Total time elapsed : 5.760000000000000E-002 4) nextp: Total permutations : 3628800 Total time elapsed : 3.600000000000000E-002 So far, we have conclusion from the above performance: 1) subnexper is the 3rd fast with ifort and the 2nd with gfortran. 2) generate is the slowest one with not only ifort but gfortran. 3) perm is the 2nd fast one with ifort and the 3rd one with gfortran. 4) nextp is the fastest one with both ifort and gfortran (the winner in this test). Note: It is worth mentioning that the performance of this test is dependent not only on algorithm, but also on computer where the test runs. Therefore we should run the test on our own computer and make conclusion by ourselves. ### Fortran 77 Here is an alternate, iterative version in Fortran 77. Translation of: Ada program nptest integer n,i,a logical nextp external nextp parameter(n=4) dimension a(n) do i=1,n a(i)=i enddo 10 print *,(a(i),i=1,n) if(nextp(n,a)) go to 10 end function nextp(n,a) integer n,a,i,j,k,t logical nextp dimension a(n) i=n-1 10 if(a(i).lt.a(i+1)) go to 20 i=i-1 if(i.eq.0) go to 20 go to 10 20 j=i+1 k=n 30 t=a(j) a(j)=a(k) a(k)=t j=j+1 k=k-1 if(j.lt.k) go to 30 j=i if(j.ne.0) go to 40 nextp=.false. return 40 j=j+1 if(a(j).lt.a(i)) go to 40 t=a(i) a(i)=a(j) a(j)=t nextp=.true. end ### Ratfor 77 See RATFOR. ## FreeBASIC ' version 07-04-2017 ' compile with: fbc -s console ' Heap's algorithm non-recursive Sub perms(n As Long) Dim As ULong i, j, count = 1 Dim As ULong a(0 To n -1), c(0 To n -1) For j = 0 To n -1 a(j) = j +1 Print a(j); Next Print " "; i = 0 While i < n If c(i) < i Then If (i And 1) = 0 Then Swap a(0), a(i) Else Swap a(c(i)), a(i) End If For j = 0 To n -1 Print a(j); Next count += 1 If count = 12 Then Print count = 0 Else Print " "; End If c(i) += 1 i = 0 Else c(i) = 0 i += 1 End If Wend End Sub ' ------=< MAIN >=------ perms(4) ' empty keyboard buffer While Inkey <> "" : Wend Print : Print "hit any key to end program" Sleep End Output: 1234 2134 3124 1324 2314 3214 4213 2413 1423 4123 2143 1243 1342 3142 4132 1432 3412 4312 4321 3421 2431 4231 3241 2341 ## Frink Frink's array class has built-in methods permute[] and lexicographicPermute[] which permute the elements of an array in reflected Gray code order and lexicographic order respectively. a = [1,2,3,4] println[formatTable[a.lexicographicPermute[]]] Output: 1 2 3 4 1 2 4 3 1 3 2 4 1 3 4 2 1 4 2 3 1 4 3 2 2 1 3 4 2 1 4 3 2 3 1 4 2 3 4 1 2 4 1 3 2 4 3 1 3 1 2 4 3 1 4 2 3 2 1 4 3 2 4 1 3 4 1 2 3 4 2 1 4 1 2 3 4 1 3 2 4 2 1 3 4 2 3 1 4 3 1 2 4 3 2 1 ## GAP GAP can handle permutations and groups. Here is a straightforward implementation : for each permutation p in S(n) (symmetric group), compute the images of 1 .. n by p. As an alternative, List(SymmetricGroup(n)) would yield the permutations as GAP Permutation objects, which would probably be more manageable in later computations. gap>List(SymmetricGroup(4), p -> Permuted([1 .. 4], p)); perms(4); [ [ 1, 2, 3, 4 ], [ 4, 2, 3, 1 ], [ 2, 4, 3, 1 ], [ 3, 2, 4, 1 ], [ 1, 4, 3, 2 ], [ 4, 1, 3, 2 ], [ 2, 1, 3, 4 ], [ 3, 1, 4, 2 ], [ 1, 3, 4, 2 ], [ 4, 3, 1, 2 ], [ 2, 3, 1, 4 ], [ 3, 4, 1, 2 ], [ 1, 2, 4, 3 ], [ 4, 2, 1, 3 ], [ 2, 4, 1, 3 ], [ 3, 2, 1, 4 ], [ 1, 4, 2, 3 ], [ 4, 1, 2, 3 ], [ 2, 1, 4, 3 ], [ 3, 1, 2, 4 ], [ 1, 3, 2, 4 ], [ 4, 3, 2, 1 ], [ 2, 3, 4, 1 ], [ 3, 4, 2, 1 ] ] GAP has also built-in functions to get permutations # All arrangements of 4 elements in 1 .. 4 Arrangements([1 .. 4], 4); # All permutations of 1 .. 4 PermutationsList([1 .. 4]); Here is an implementation using a function to compute next permutation in lexicographic order: NextPermutation := function(a) local i, j, k, n, t; n := Length(a); i := n - 1; while i > 0 and a[i] > a[i + 1] do i := i - 1; od; j := i + 1; k := n; while j < k do t := a[j]; a[j] := a[k]; a[k] := t; j := j + 1; k := k - 1; od; if i = 0 then return false; else j := i + 1; while a[j] < a[i] do j := j + 1; od; t := a[i]; a[i] := a[j]; a[j] := t; return true; fi; end; Permutations := function(n) local a, L; a := List([1 .. n], x -> x); L := [ ]; repeat Add(L, ShallowCopy(a)); until not NextPermutation(a); return L; end; Permutations(3); [ [ 1, 2, 3 ], [ 1, 3, 2 ], [ 2, 1, 3 ], [ 2, 3, 1 ], [ 3, 1, 2 ], [ 3, 2, 1 ] ] ## Glee $$n !! k dyadic: Permutations for k out of n elements (in this case k = n)$$ #s monadic: number of elements in s $$,, monadic: expose with space-lf separators$$ s[n] index n of s 'Hello' 123 7.9 '•'=>s; s[s# !! (s#)],, Result: Hello 123 7.9 • Hello 123 • 7.9 Hello 7.9 123 • Hello 7.9 • 123 Hello • 123 7.9 Hello • 7.9 123 123 Hello 7.9 • 123 Hello • 7.9 123 7.9 Hello • 123 7.9 • Hello 123 • Hello 7.9 123 • 7.9 Hello 7.9 Hello 123 • 7.9 Hello • 123 7.9 123 Hello • 7.9 123 • Hello 7.9 • Hello 123 7.9 • 123 Hello • Hello 123 7.9 • Hello 7.9 123 • 123 Hello 7.9 • 123 7.9 Hello • 7.9 Hello 123 • 7.9 123 Hello ## GNU make Recursive on unique elements #delimiter should not occur inside elements delimiter=; #convert list to delimiter separated string implode=$(subst $()$(),$(delimiter),$(strip $1)) #convert delimiter separated string to list explode=$(strip $(subst$(delimiter), ,$1)) #enumerate all permutations and subpermutations permutations0=$(if $1,$(foreach x,$1,$x $(addprefix$x$(delimiter),$(call permutations0,$(filter-out$x,$1)))),) #remove subpermutations from permutations0 output permutations=$(strip $(foreach x,$(call permutations0,$1),$(if $(filter$(words $1),$(words $(call explode,$x))),$(call implode,$(call explode,$x)),))) delimiter_separated_output=$(call permutations,a b c d)
$(info$(delimiter_separated_output))

Output:
a;b;c;d a;b;d;c a;c;b;d a;c;d;b a;d;b;c a;d;c;b b;a;c;d b;a;d;c b;c;a;d b;c;d;a b;d;a;c b;d;c;a c;a;b;d c;a;d;b c;b;a;d c;b;d;a c;d;a;b c;d;b;a d;a;b;c d;a;c;b d;b;a;c d;b;c;a d;c;a;b d;c;b;a

## Go

### recursive

package main

import "fmt"

func main() {
demoPerm(3)
}

func demoPerm(n int) {
// create a set to permute. for demo, use the integers 1..n.
s := make([]int, n)
for i := range s {
s[i] = i + 1
}
// permute them, calling a function for each permutation.
// for demo, function just prints the permutation.
permute(s, func(p []int) { fmt.Println(p) })
}

// permute function. takes a set to permute and a function
// to call for each generated permutation.
func permute(s []int, emit func([]int)) {
if len(s) == 0 {
emit(s)
return
}
// Steinhaus, implemented with a recursive closure.
// arg is number of positions left to permute.
// pass in len(s) to start generation.
// on each call, weave element at pp through the elements 0..np-2,
// then restore array to the way it was.
var rc func(int)
rc = func(np int) {
if np == 1 {
emit(s)
return
}
np1 := np - 1
pp := len(s) - np1
// weave
rc(np1)
for i := pp; i > 0; i-- {
s[i], s[i-1] = s[i-1], s[i]
rc(np1)
}
// restore
w := s[0]
copy(s, s[1:pp+1])
s[pp] = w
}
rc(len(s))
}
Output:
[1 2 3]
[1 3 2]
[3 1 2]
[2 1 3]
[2 3 1]
[3 2 1]

### non-recursive, lexicographical order

package main

import "fmt"

func main() {
var a = []int{1, 2, 3}
fmt.Println(a)
var n = len(a) - 1
var i, j int
for c := 1; c < 6; c++ { // 3! = 6:
i = n - 1
j = n
for a[i] > a[i+1] {
i--
}
for a[j] < a[i] {
j--
}
a[i], a[j] = a[j], a[i]
j = n
i += 1
for i < j {
a[i], a[j] = a[j], a[i]
i++
j--
}
fmt.Println(a)
}
}
Output:
[1 2 3]
[1 3 2]
[2 1 3]
[2 3 1]
[3 1 2]
[3 2 1]

## Groovy

Solution:

def makePermutations = { l -> l.permutations() }

Test:

def list = ['Crosby', 'Stills', 'Nash', 'Young']
def permutations = makePermutations(list)
assert permutations.size() == (1..<(list.size()+1)).inject(1) { prod, i -> prod*i }
permutations.each { println it }
Output:
[Young, Crosby, Stills, Nash]
[Crosby, Stills, Young, Nash]
[Nash, Crosby, Young, Stills]
[Stills, Nash, Crosby, Young]
[Young, Stills, Crosby, Nash]
[Stills, Crosby, Nash, Young]
[Stills, Crosby, Young, Nash]
[Stills, Young, Nash, Crosby]
[Nash, Stills, Young, Crosby]
[Crosby, Young, Nash, Stills]
[Crosby, Nash, Young, Stills]
[Crosby, Nash, Stills, Young]
[Nash, Young, Stills, Crosby]
[Young, Nash, Stills, Crosby]
[Nash, Young, Crosby, Stills]
[Young, Stills, Nash, Crosby]
[Crosby, Stills, Nash, Young]
[Stills, Young, Crosby, Nash]
[Young, Nash, Crosby, Stills]
[Nash, Stills, Crosby, Young]
[Young, Crosby, Nash, Stills]
[Nash, Crosby, Stills, Young]
[Crosby, Young, Stills, Nash]
[Stills, Nash, Young, Crosby]

import Data.List (permutations)

main = mapM_ print (permutations [1,2,3])

A simple implementation, that assumes elements are unique and support equality:

import Data.List (delete)

permutations :: Eq a => [a] -> [[a]]
permutations [] = [[]]
permutations xs = [ x:ys | x <- xs, ys <- permutations (delete x xs)]

A slightly more efficient implementation that doesn't have the above restrictions:

permutations :: [a] -> [[a]]
permutations [] = [[]]
permutations xs = [ y:zs | (y,ys) <- select xs, zs <- permutations ys]
where select [] = []
select (x:xs) = (x,xs) : [ (y,x:ys) | (y,ys) <- select xs ]

The above are all selection-based approaches. The following is an insertion-based approach:

permutations :: [a] -> [[a]]
permutations = foldr (concatMap . insertEverywhere) [[]]
where insertEverywhere :: a -> [a] -> [[a]]
insertEverywhere x [] = [[x]]
insertEverywhere x l@(y:ys) = (x:l) : map (y:) (insertEverywhere x ys)

A serialized version:

Translation of: Mathematica
import Data.Bifunctor (second)

permutations :: [a] -> [[a]]
permutations =
let ins x xs n = uncurry (<>) $second (x :) (splitAt n xs) in foldr ( \x a -> a >>= (fmap . ins x) <*> (enumFromTo 0 . length) ) [[]] main :: IO () main = print$ permutations [1, 2, 3]
Output:
[[1,2,3],[2,3,1],[3,1,2],[2,1,3],[1,3,2],[3,2,1]]

## Icon and Unicon

procedure main(A)
every p := permute(A) do every writes((!p||" ")|"\n")
end

procedure permute(A)
if *A <= 1 then return A
suspend [(A[1]<->A[i := 1 to *A])] ||| permute(A[2:0])
end
Output:
->permute Aardvarks eat ants
Aardvarks eat ants
Aardvarks ants eat
eat Aardvarks ants
eat ants Aardvarks
ants eat Aardvarks
ants Aardvarks eat
->

## IS-BASIC

100 PROGRAM "Permutat.bas"
110 LET N=4 ! Number of elements
120 NUMERIC T(1 TO N)
130 FOR I=1 TO N
140 LET T(I)=I
150 NEXT
160 LET S=0
170 CALL PERM(N)
180 PRINT "Number of permutations:";S
190 END
200 DEF PERM(I)
210 NUMERIC J,X
220 IF I=1 THEN
230 FOR X=1 TO N
240 PRINT T(X);
250 NEXT
260 PRINT :LET S=S+1
270 ELSE
280 CALL PERM(I-1)
290 FOR J=1 TO I-1
300 LET C=T(J):LET T(J)=T(I):LET T(I)=C
310 CALL PERM(I-1)
320 LET C=T(J):LET T(J)=T(I):LET T(I)=C
330 NEXT
340 END IF
350 END DEF

## J

perms=: A.&i.~ !
Example use:
perms 2
0 1
1 0
({~ [email protected]#)&.;: 'some random text'
some random text
some text random
random some text
random text some
text some random
text random some

## Java

Using the code of Michael Gilleland.

public class PermutationGenerator {
private int[] array;
private int firstNum;

public PermutationGenerator(int n, int firstNum_) {
if (n < 1) {
throw new IllegalArgumentException("The n must be min. 1");
}
firstNum = firstNum_;
array = new int[n];
reset();
}

public void reset() {
for (int i = 0; i < array.length; i++) {
array[i] = i + firstNum;
}
}

public boolean hasMore() {
for (int i = 1; i < array.length; i++) {
end = end && array[i] < array[i-1];
}
return !end;
}

public int[] getNext() {

return array;
}

int temp;
int j = array.length - 2;
int k = array.length - 1;

// Find largest index j with a[j] < a[j+1]

for (;array[j] > array[j+1]; j--);

// Find index k such that a[k] is smallest integer
// greater than a[j] to the right of a[j]

for (;array[j] > array[k]; k--);

// Interchange a[j] and a[k]

temp = array[k];
array[k] = array[j];
array[j] = temp;

// Put tail end of permutation after jth position in increasing order

int r = array.length - 1;
int s = j + 1;

while (r > s) {
temp = array[s];
array[s++] = array[r];
array[r--] = temp;
}

return array;
} // getNext()

// For testing of the PermutationGenerator class
public static void main(String[] args) {
PermutationGenerator pg = new PermutationGenerator(3, 1);

while (pg.hasMore()) {
int[] temp = pg.getNext();
for (int i = 0; i < temp.length; i++) {
System.out.print(temp[i] + " ");
}
System.out.println();
}
}

} // class
Output:
1 2 3
1 3 2
2 1 3
2 3 1
3 1 2
3 2 1

optimized

Following needs: Utils.java

public class Permutations {
public static void main(String[] args) {
System.out.println(Utils.Permutations(Utils.mRange(1, 3)));
}
}
Output:
[[1, 2, 3], [1, 3, 2], [2, 1, 3], [2, 3, 1], [3, 1, 2], [3, 2, 1]]

## JavaScript

### ES5

#### Iteration

Copy the following as an HTML file and load in a browser.

<body><pre id="result"></pre>
<script type="text/javascript">
var d = document.getElementById('result');

function perm(list, ret)
{
if (list.length == 0) {
var row = document.createTextNode(ret.join(' ') + '\n');
d.appendChild(row);
return;
}
for (var i = 0; i < list.length; i++) {
var x = list.splice(i, 1);
ret.push(x);
perm(list, ret);
ret.pop();
list.splice(i, 0, x);
}
}

perm([1, 2, 'A', 4], []);
</script></body></html>

Alternatively: 'Genuine' js code, assuming no duplicate.

function perm(a) {
if (a.length < 2) return [a];
var c, d, b = [];
for (c = 0; c < a.length; c++) {
var e = a.splice(c, 1),
f = perm(a);
for (d = 0; d < f.length; d++) b.push([e].concat(f[d]));
a.splice(c, 0, e[0])
} return b
}

console.log(perm(['Aardvarks', 'eat', 'ants']).join("\n"));

Output:
Aardvarks,eat,ants
Aardvarks,ants,eat
eat,Aardvarks,ants
eat,ants,Aardvarks
ants,Aardvarks,eat
ants,eat,Aardvarks

#### Functional composition

(Simple version – assuming a unique list of objects comparable by the JS === operator)

(function () {
'use strict';

// permutations :: [a] -> [[a]]
var permutations = function (xs) {
return xs.length ? concatMap(function (x) {
return concatMap(function (ys) {
return [[x].concat(ys)];
}, permutations(delete_(x, xs)));
}, xs) : [[]];
};

// GENERIC FUNCTIONS

// concatMap :: (a -> [b]) -> [a] -> [b]
var concatMap = function (f, xs) {
return [].concat.apply([], xs.map(f));
};

// delete :: Eq a => a -> [a] -> [a]
var delete_ = function (x, xs) {
return deleteBy(function (a, b) {
return a === b;
}, x, xs);
};

// deleteBy :: (a -> a -> Bool) -> a -> [a] -> [a]
var deleteBy = function (f, x, xs) {
return xs.length > 0 ? f(x, xs[0]) ? xs.slice(1) :
[xs[0]].concat(deleteBy(f, x, xs.slice(1))) : [];
};

// TEST
return permutations(['Aardvarks', 'eat', 'ants']);
})();
Output:
[["Aardvarks", "eat", "ants"], ["Aardvarks", "ants", "eat"],
["eat", "Aardvarks", "ants"], ["eat", "ants", "Aardvarks"],
["ants", "Aardvarks", "eat"], ["ants", "eat", "Aardvarks"]]

### ES6

Recursively, in terms of concatMap and delete:

(() => {
'use strict';

// permutations :: [a] -> [[a]]
const permutations = xs => {
const go = xs => xs.length ? (
concatMap(
x => concatMap(
ys => [[x].concat(ys)],
go(delete_(x, xs))), xs
)
) : [[]];
return go(xs);
};

// GENERIC FUNCTIONS ----------------------------------

// concatMap :: (a -> [b]) -> [a] -> [b]
const concatMap = (f, xs) =>
xs.reduce((a, x) => a.concat(f(x)), []);

// delete :: Eq a => a -> [a] -> [a]
const delete_ = (x, xs) => {
const go = xs => {
return 0 < xs.length ? (
(x === xs[0]) ? (
xs.slice(1)
) : [xs[0]].concat(go(xs.slice(1)))
) : [];
}
return go(xs);
};

// TEST
return JSON.stringify(
permutations(['Aardvarks', 'eat', 'ants'])
);
})();
Output:
[["Aardvarks", "eat", "ants"], ["Aardvarks", "ants", "eat"],
["eat", "Aardvarks", "ants"], ["eat", "ants", "Aardvarks"],
["ants", "Aardvarks", "eat"], ["ants", "eat", "Aardvarks"]]

Or, without recursion, in terms of concatMap and reduce:

(() => {
'use strict';

// permutations :: [a] -> [[a]]
const permutations = xs =>
xs.reduceRight(
(a, x) => concatMap(
xs => enumFromTo(0, xs.length)
.map(n => xs.slice(0, n)
.concat(x)
.concat(xs.slice(n))
),
a
),
[[]]
);

// GENERIC FUNCTIONS ----------------------------------

// concatMap :: (a -> [b]) -> [a] -> [b]
const concatMap = (f, xs) =>
xs.reduce((a, x) => a.concat(f(x)), []);

// ft :: Int -> Int -> [Int]
const enumFromTo = (m, n) =>
Array.from({
length: 1 + n - m
}, (_, i) => m + i);

// showLog :: a -> IO ()
const showLog = (...args) =>
console.log(
args
.map(JSON.stringify)
.join(' -> ')
);

// TEST -----------------------------------------------
showLog(
permutations([1, 2, 3])
);
})();
Output:
[[1,2,3],[2,1,3],[2,3,1],[1,3,2],[3,1,2],[3,2,1]]

## jq

"permutations" generates a stream of the permutations of the input array.

def permutations:
if length == 0 then []
else
range(0;length) as $i | [.[$i]] + (del(.[$i])|permutations) end ; Example 1: list them [range(0;3)] | permutations [0,1,2] [0,2,1] [1,0,2] [1,2,0] [2,0,1] [2,1,0] Example 2: count them [[range(0;3)] | permutations] | length 6 Or more efficiently: def count(s): reduce s as$i (0;.+1);
[range(0;3)] | count(permutations)
6

Example 3: 10!

[range(0;10)] | count(permutations)
3628800

## Julia

julia> perms(l) = isempty(l) ? [l] : [[x; y] for x in l for y in perms(setdiff(l, x))]

Output:

julia> perms([1,2,3])
6-element Vector{Vector{Int64}}:
[1, 2, 3]
[1, 3, 2]

[3, 1, 2]
[3, 2, 1]

Further support for permutation creation and processing is available in the Combinatorics.jl package. permutations(v) creates an iterator over all permutations of v. Julia 0.7 and 1.0+ require the line global i inside the for to update the i variable.

using Combinatorics

term = "RCode"
i = 0
pcnt = factorial(length(term))
print("All the permutations of ", term, " (", pcnt, "):\n ")
for p in permutations(split(term, ""))
global i
print(join(p), " ")
i += 1
i %= 12
i != 0 || print("\n ")
end
println()

Output:
All the permutations of RCode (120):
RCode RCoed RCdoe RCdeo RCeod RCedo RoCde RoCed RodCe RodeC RoeCd RoedC
RdCoe RdCeo RdoCe RdoeC RdeCo RdeoC ReCod ReCdo ReoCd ReodC RedCo RedoC
CRode CRoed CRdoe CRdeo CReod CRedo CoRde CoRed CodRe CodeR CoeRd CoedR
CdRoe CdReo CdoRe CdoeR CdeRo CdeoR CeRod CeRdo CeoRd CeodR CedRo CedoR
oRCde oRCed oRdCe oRdeC oReCd oRedC oCRde oCRed oCdRe oCdeR oCeRd oCedR
odRCe odReC odCRe odCeR odeRC odeCR oeRCd oeRdC oeCRd oeCdR oedRC oedCR
dRCoe dRCeo dRoCe dRoeC dReCo dReoC dCRoe dCReo dCoRe dCoeR dCeRo dCeoR
doRCe doReC doCRe doCeR doeRC doeCR deRCo deRoC deCRo deCoR deoRC deoCR
eRCod eRCdo eRoCd eRodC eRdCo eRdoC eCRod eCRdo eCoRd eCodR eCdRo eCdoR
eoRCd eoRdC eoCRd eoCdR eodRC eodCR edRCo edRoC edCRo edCoR edoRC edoCR

# Generate all permutations of size t from an array a with possibly duplicated elements.
collect(Combinatorics.multiset_permutations([1,1,0,0,0],3))

Output:
7-element Array{Array{Int64,1},1}:
[1, 1, 0]
[1, 0, 1]
[1, 0, 0]
[0, 1, 1]
[0, 1, 0]
[0, 0, 1]
[0, 0, 0]

## K

Translation of: J
perm:{:[1<x;,/(>:'(x,x)#1,x#0)[;0,'1+_f x-1];,!x]}
perm 2
(0 1
1 0)

0:{1_,/" ",/:x}'[email protected]@#r:("some";"random";"text")
some random text
some text random
random some text
random text some
text some random
text random some

Alternative:

perm:{[email protected]@&n=(#?:)'m:!n#n:#x}

perm[!3]
(0 1 2
0 2 1
1 0 2
1 2 0
2 0 1
2 1 0)

perm "abc"
("abc"
"acb"
"bac"
"bca"
"cab"
"cba")

0:{1_,/" ",/: $x}' perm $" "\"some random text"
some random text
some text random
random some text
random text some
text some random
text random some

## Kotlin

Translation of C# recursive 'insert' solution in Wikipedia article on Permutations:

// version 1.1.2

fun <T> permute(input: List<T>): List<List<T>> {
if (input.size == 1) return listOf(input)
val perms = mutableListOf<List<T>>()
val toInsert = input[0]
for (perm in permute(input.drop(1))) {
for (i in 0..perm.size) {
val newPerm = perm.toMutableList()
}
}
return perms
}

fun main(args: Array<String>) {
val input = listOf('a', 'b', 'c', 'd')
val perms = permute(input)
println("There are ${perms.size} permutations of$input, namely:\n")
for (perm in perms) println(perm)
}
Output:
There are 24 permutations of [a, b, c, d], namely:

[a, b, c, d]
[b, a, c, d]
[b, c, a, d]
[b, c, d, a]
[a, c, b, d]
[c, a, b, d]
[c, b, a, d]
[c, b, d, a]
[a, c, d, b]
[c, a, d, b]
[c, d, a, b]
[c, d, b, a]
[a, b, d, c]
[b, a, d, c]
[b, d, a, c]
[b, d, c, a]
[a, d, b, c]
[d, a, b, c]
[d, b, a, c]
[d, b, c, a]
[a, d, c, b]
[d, a, c, b]
[d, c, a, b]
[d, c, b, a]

## Lambdatalk

{def inject
{lambda {:x :a}
{if {A.empty? :a}
then {A.new {A.new :x}}
else {let { {:c {{lambda {:a :b} {A.cons {A.first :a} :b}} :a}}
{:d {inject :x {A.rest :a}}}
{:e {A.cons :x :a}}
} {A.cons :e {A.map :c :d}}}}}}
-> inject

{def permut
{lambda {:a}
{if {A.empty? :a}
then {A.new :a}
else {let { {:c {{lambda {:a :b} {inject {A.first :a} :b}} :a}}
{:d {permut {A.rest :a}}}
} {A.reduce A.concat {A.map :c :d}}}}}}
-> permut

{permut {A.new 1 2 3}}
-> [[1,2,3],[2,1,3],[2,3,1],[1,3,2],[3,1,2],[3,2,1]]

{permut {A.new 1 2 3 4}}
->
[[1,2,3,4],[2,1,3,4],[2,3,1,4],[2,3,4,1],[1,3,2,4],[3,1,2,4],[3,2,1,4],[3,2,4,1],[1,3,4,2],[3,1,4,2],[3,4,1,2],[3,4,2,1],[1,2,4,3],[2,1,4,3],[2,4,1,3],[2,4,3,1],[1,4,2,3],[4,1,2,3],[4,2,1,3],[4,2,3,1],[1,4,3,2],[4,1,3,2],[4,3,1,2],[4,3,2,1]]

And this is an illustration of the way lambdatalk builds an interface for javascript functions (the first one is given in this page):

1) permutations on sentences

{script
var S_perm = function(a) {
if (a.length < 2) return [a];
var b = [];
for (var c = 0; c < a.length; c++) {
var e = a.splice(c, 1), f = S_perm(a);
for (var d = 0; d < f.length; d++)
b.push( e.concat( f[d]) );
a.splice(c, 0, e[0])
}
return b
}

LAMBDATALK.DICT['S.perm'] = function() { // {S.perm 1 2 3}
return S_perm( arguments[0].trim()
.split(" ") )
.join(" ")
.replace(/\s/g,"{br}")
};
}

{S.perm 1 2 3}
->
1,2,3
1,3,2
2,1,3
2,3,1
3,1,2
3,2,1

{S.perm hello brave world}
->
hello,brave,world
hello,world,brave
brave,hello,world
brave,world,hello
world,hello,brave
world,brave,hello

2) permutations on words

{script
var W_perm = function(word) {
if (word.length === 1) return [word]
var results = [];
for (var i = 0; i < word.length; i++) {
var buti = W_perm( word.substring(0, i) + word.substring(i + 1) );
for (var j = 0; j < buti.length; j++)
results.push(word[i] + buti[j]);
}
return results;
};

LAMBDATALK.DICT['W.perm'] = function() { // {W.perm 123}
return W_perm( arguments[0].trim() ).join("{br}")
};

}

{W.perm 123}
->
123
132
213
231
312
321

## langur

Translation of: Go

This follows the Go language non-recursive example, but is not limited to integers, or even to numbers.

Works with: langur version 0.10

Prior to 0.10, multi-variable declaration/assignment would use parentheses around variable names and values. 0.10 also parses the increment section of a for loop as a multi-variable assignment, not as a list of assignments.

val .factorial = f if(.x < 2: 1; .x x self(.x - 1))

val .permute = f(.arr) {
if not isArray(.arr): throw "expected array"

val .limit = 10
if len(.arr) > .limit: throw $"permutation limit exceeded (currently \.limit;)" var .elements = .arr var .ordinals = pseries len .elements val .n = len(.ordinals) var .i, .j for[.p=[.arr]] of .factorial(len .arr)-1 { .i = .n - 1 .j = .n while .ordinals[.i] > .ordinals[.i+1] { .i -= 1 } while .ordinals[.j] < .ordinals[.i] { .j -= 1 } .ordinals[.i], .ordinals[.j] = .ordinals[.j], .ordinals[.i] .elements[.i], .elements[.j] = .elements[.j], .elements[.i] .i += 1 for .j = .n; .i < .j ; .i, .j = .i+1, .j-1 { .ordinals[.i], .ordinals[.j] = .ordinals[.j], .ordinals[.i] .elements[.i], .elements[.j] = .elements[.j], .elements[.i] } .p = more .p, .elements } } for .e in .permute([1, 3.14, 7]) { writeln .e } Output: [1, 3.14, 7] [1, 7, 3.14] [3.14, 1, 7] [3.14, 7, 1] [7, 1, 3.14] [7, 3.14, 1] ## LFE (defun permute (('()) '(())) ((l) (lc ((<- x l) (<- y (permute (-- l (,x))))) (cons x y)))) REPL usage: > (permute '(1 2 3)) ((1 2 3) (1 3 2) (2 1 3) (2 3 1) (3 1 2) (3 2 1)) ## Liberty BASIC Permuting numerical array (non-recursive): Translation of: PowerBASIC n=3 dim a(n+1) '+1 needed due to bug in LB that checks loop condition ' until (i=0) or (a(i)<a(i+1)) 'before executing i=i-1 in loop body. for i=1 to n: a(i)=i: next do for i=1 to n: print a(i);: next: print i=n do i=i-1 loop until (i=0) or (a(i)<a(i+1)) j=i+1 k=n while j<k 'swap a(j),a(k) tmp=a(j): a(j)=a(k): a(k)=tmp j=j+1 k=k-1 wend if i>0 then j=i+1 while a(j)<a(i) j=j+1 wend 'swap a(i),a(j) tmp=a(j): a(j)=a(i): a(i)=tmp end if loop until i=0 Output: 123 132 213 231 312 321 Permuting string (recursive): n = 3 s$=""
for i = 1 to n
s$=s$;i
next

res$=permutation$("", s$) Function permutation$(pre$, post$)
lgth = Len(post$) If lgth < 2 Then print pre$;post$Else For i = 1 To lgth tmp$=permutation$(pre$+Mid$(post$,i,1),Left$(post$,i-1)+Right$(post$,lgth-i))
Next i
End If
End Function

Output:
123
132
213
231
312
321

## Lobster

// Lobster implementation of the (very fast) Go example
// http://rosettacode.org/wiki/Permutations#Go
// implementing the plain changes (bell ringers) algorithm, using a recursive function
// https://en.wikipedia.org/wiki/Steinhaus–Johnson–Trotter_algorithm

def permr(s, f):
if s.length == 0:
f(s)
return
def rc(np: int):
if np == 1:
f(s)
return
let np1 = np - 1
let pp = s.length - np1
rc(np1) // recurs prior swaps
var i = pp
while i > 0:
// swap s[i], s[i-1]
let t = s[i]
s[i] = s[i-1]
s[i-1] = t
rc(np1) // recurs swap
i -= 1
let w = s[0]
for(pp): s[_] = s[_+1]
s[pp] = w
rc(s.length)

// Heap's recursive method https://en.wikipedia.org/wiki/Heap%27s_algorithm

def permh(s, f):
def rc(k: int):
if k <= 1:
f(s)
else:
// Generate permutations with kth unaltered
// Initially k == length(s)
rc(k-1)
// Generate permutations for kth swapped with each k-1 initial
for(k-1) i:
// Swap choice dependent on parity of k (even or odd)
// zero-indexed, the kth is at k-1
if (k & 1) == 0:
let t = s[i]
s[i] = s[k-1]
s[k-1] = t
else:
let t = s[0]
s[0] = s[k-1]
s[k-1] = t
rc(k-1)
rc(s.length)

// iterative Boothroyd method

import std

def permi(xs, f):
var d = 1
let c = map(xs.length): 0
f(xs)
while true:
while d > 1:
d -= 1
c[d] = 0
while c[d] >= d:
d += 1
if d >= xs.length:
return
let i = if (d & 1) == 1: c[d] else: 0
let t = xs[i]
xs[i] = xs[d]
xs[d] = t
f(xs)
c[d] = c[d] + 1

// next lexicographical permutation
// to get all permutations the initial input a must be in sorted order
// returns false when input a is in reverse sorted order

def next_lex_perm(a):
def swap(i, j):
let t = a[i]
a[i] = a[j]
a[j] = t
let n = a.length
/* 1. Find the largest index k such that a[k] < a[k + 1]. If no such
index exists, the permutation is the last permutation. */
var k = n - 1
while k > 0 and a[k-1] >= a[k]: k--
if k == 0: return false
k -= 1
/* 2. Find the largest index l such that a[k] < a[l]. Since k + 1 is
such an index, l is well defined */
var l = n - 1
while a[l] <= a[k]: l--
/* 3. Swap a[k] with a[l] */
swap(k, l)
/* 4. Reverse the sequence from a[k + 1] to the end */
k += 1
l = n - 1
while l > k:
swap(k, l)
l -= 1
k += 1
return true

var se = [0, 1, 2, 3] //, 4, 5, 6, 7, 8, 9, 10]

print "Iterative lexicographical permuter"

print se
while next_lex_perm(se): print se

print "Recursive plain changes iterator"

se = [0, 1, 2, 3]

permr(se): print(_)

print "Recursive Heap\'s iterator"

se = [0, 1, 2, 3]

permh(se): print(_)

print "Iterative Boothroyd iterator"

se = [0, 1, 2, 3]

permi(se): print(_)

Output:
Iterative lexicographical permuter
[0, 1, 2, 3]
[0, 1, 3, 2]
[0, 2, 1, 3]
[0, 2, 3, 1]
[0, 3, 1, 2]
[0, 3, 2, 1]
[1, 0, 2, 3]
[1, 0, 3, 2]
[1, 2, 0, 3]
[1, 2, 3, 0]
[1, 3, 0, 2]
[1, 3, 2, 0]
[2, 0, 1, 3]
[2, 0, 3, 1]
[2, 1, 0, 3]
[2, 1, 3, 0]
[2, 3, 0, 1]
[2, 3, 1, 0]
[3, 0, 1, 2]
[3, 0, 2, 1]
[3, 1, 0, 2]
[3, 1, 2, 0]
[3, 2, 0, 1]
[3, 2, 1, 0]
Recursive plain changes iterator
[0, 1, 2, 3]
[0, 1, 3, 2]
[0, 3, 1, 2]
[3, 0, 1, 2]
[0, 2, 1, 3]
[0, 2, 3, 1]
[0, 3, 2, 1]
[3, 0, 2, 1]
[2, 0, 1, 3]
[2, 0, 3, 1]
[2, 3, 0, 1]
[3, 2, 0, 1]
[1, 0, 2, 3]
[1, 0, 3, 2]
[1, 3, 0, 2]
[3, 1, 0, 2]
[1, 2, 0, 3]
[1, 2, 3, 0]
[1, 3, 2, 0]
[3, 1, 2, 0]
[2, 1, 0, 3]
[2, 1, 3, 0]
[2, 3, 1, 0]
[3, 2, 1, 0]
Recursive Heap's iterator
[0, 1, 2, 3]
[1, 0, 2, 3]
[2, 0, 1, 3]
[0, 2, 1, 3]
[1, 2, 0, 3]
[2, 1, 0, 3]
[3, 1, 0, 2]
[1, 3, 0, 2]
[0, 3, 1, 2]
[3, 0, 1, 2]
[1, 0, 3, 2]
[0, 1, 3, 2]
[0, 2, 3, 1]
[2, 0, 3, 1]
[3, 0, 2, 1]
[0, 3, 2, 1]
[2, 3, 0, 1]
[3, 2, 0, 1]
[3, 2, 1, 0]
[2, 3, 1, 0]
[1, 3, 2, 0]
[3, 1, 2, 0]
[2, 1, 3, 0]
[1, 2, 3, 0]
Iterative Boothroyd iterator
[0, 1, 2, 3]
[1, 0, 2, 3]
[2, 0, 1, 3]
[0, 2, 1, 3]
[1, 2, 0, 3]
[2, 1, 0, 3]
[3, 1, 0, 2]
[1, 3, 0, 2]
[0, 3, 1, 2]
[3, 0, 1, 2]
[1, 0, 3, 2]
[0, 1, 3, 2]
[0, 2, 3, 1]
[2, 0, 3, 1]
[3, 0, 2, 1]
[0, 3, 2, 1]
[2, 3, 0, 1]
[3, 2, 0, 1]
[3, 2, 1, 0]
[2, 3, 1, 0]
[1, 3, 2, 0]
[3, 1, 2, 0]
[2, 1, 3, 0]
[1, 2, 3, 0]

## Logtalk

:- object(list).

:- public(permutation/2).

permutation(List, Permutation) :-
same_length(List, Permutation),
permutation2(List, Permutation).

permutation2([], []).
permutation2(Remaining, Tail).

same_length([], []).
same_length([_| Tail1], [_| Tail2]) :-
same_length(Tail1, Tail2).

:- end_object.
Usage example:
| ?- forall(list::permutation([1, 2, 3], Permutation), (write(Permutation), nl)).

[1,2,3]
[1,3,2]
[2,1,3]
[2,3,1]
[3,1,2]
[3,2,1]
yes

## Lua

local function permutation(a, n, cb)
if n == 0 then
cb(a)
else
for i = 1, n do
a[i], a[n] = a[n], a[i]
permutation(a, n - 1, cb)
a[i], a[n] = a[n], a[i]
end
end
end

--Usage
local function callback(a)
print('{'..table.concat(a, ', ')..'}')
end
permutation({1,2,3}, 3, callback)

Output:
{2, 3, 1}
{3, 2, 1}
{3, 1, 2}
{1, 3, 2}
{2, 1, 3}
{1, 2, 3}

-- Iterative version
function ipermutations(a,b)
if a==0 then return end
local taken = {} local slots = {}
for i=1,a do slots[i]=0 end
for i=1,b do taken[i]=false end
local index = 1
while index > 0 do repeat
repeat slots[index] = slots[index] + 1
until slots[index] > b or not taken[slots[index]]
if slots[index] > b then
slots[index] = 0
index = index - 1
if index > 0 then
taken[slots[index]] = false
end
break
else
taken[slots[index]] = true
end
if index == a then
for i=1,a do io.write(slots[i]) io.write(" ") end
io.write("\n")
taken[slots[index]] = false
break
end
index = index + 1
until true end
end

ipermutations(3, 3)

1 2 3
1 3 2
2 1 3
2 3 1
3 1 2
3 2 1

### fast, iterative with coroutine to use as a generator

#!/usr/bin/env luajit
-- Iterative version
local function ipermgen(a,b)
if a==0 then return end
local taken = {} local slots = {}
for i=1,a do slots[i]=0 end
for i=1,b do taken[i]=false end
local index = 1
while index > 0 do repeat
repeat slots[index] = slots[index] + 1
until slots[index] > b or not taken[slots[index]]
if slots[index] > b then
slots[index] = 0
index = index - 1
if index > 0 then
taken[slots[index]] = false
end
break
else
taken[slots[index]] = true
end
if index == a then
coroutine.yield(slots)
taken[slots[index]] = false
break
end
index = index + 1
until true end
end
local function iperm(a)
local co=coroutine.create(function() ipermgen(a,a) end)
return function()
local code,res=coroutine.resume(co)
return res
end
end

local a=arg[1] and tonumber(arg[1]) or 3
for p in iperm(a) do
print(table.concat(p, " "))
end

Output:
> ./perm_iter_coroutine.lua 3
1 2 3
1 3 2
2 1 3
2 3 1
3 1 2
3 2 1

## M2000 Interpreter

### All permutations in one module

Module Checkit {
Global a$Document a$
Module Permutations (s){
Module Level (n, s, h) {
If n=1 then {
while Len(s) {
m1=each(h)
while m1 {
Print Array$(m1);" "; } Print Array$(S)
ToClipBoard()
s=cdr(s)
}
} Else {
for i=1 to len(s) {
call Level n-1, cdr(s), cons(h, car(s))
s=cons(cdr(s), car(s))
}
}
Sub ToClipBoard()
local m=each(h)
Local b$="" While m { b$+=If$(Len(b$)<>0->" ","")+Array$(m)+" " } b$+=If$(Len(b$)<>0->" ","")+Array$(s,0)+" "+{ } a$<=b$' assign to global need <= End Sub } If len(s)=0 then Error Head=(,) Call Level Len(s), s, Head } Clear a$
Permutations (1,2,3,4)
Permutations (100, 200, 500)
Permutations ("A", "B", "C","D")
Permutations ("DOG", "CAT", "BAT")
ClipBoard a$} Checkit ### Step by step Generator Module StepByStep { Function PermutationStep (a) { c1=lambda (&f, a) ->{ =car(a) f=true } m=len(a) c=c1 while m>1 { c1=lambda c2=c,p, m=(,) (&f, a) ->{ if len(m)=0 then m=a =cons(car(m),c2(&f, cdr(m))) if f then f=false:p++: m=cons(cdr(m), car(m)) : if p=len(m) then p=0 : m=(,):: f=true } c=c1 m-- } =lambda c, a (&f) -> { =c(&f, a) } } k=false StepA=PermutationStep((1,2,3,4)) while not k { Print StepA(&k) } k=false StepA=PermutationStep((100,200,300)) while not k { Print StepA(&k) } k=false StepA=PermutationStep(("A", "B", "C", "D")) while not k { Print StepA(&k) } k=false StepA=PermutationStep(("DOG", "CAT", "BAT")) while not k { Print StepA(&k) } } StepByStep Output: 1 2 3 4 1 2 4 3 1 3 4 2 1 3 2 4 1 4 2 3 1 4 3 2 2 3 4 1 2 3 1 4 2 4 1 3 2 4 3 1 2 1 3 4 2 1 4 3 3 4 1 2 3 4 2 1 3 1 2 4 3 1 4 2 3 2 4 1 3 2 1 4 4 1 2 3 4 1 3 2 4 2 3 1 4 2 1 3 4 3 1 2 4 3 2 1 100 200 500 100 500 200 200 500 100 200 100 500 500 100 200 500 200 100 A B C D A B D C A C D B A C B D A D B C A D C B B C D A B C A D B D A C B D C A B A C D B A D C C D A B C D B A C A B D C A D B C B D A C B A D D A B C D A C B D B C A D B A C D C A B D C B A DOG CAT BAT DOG BAT CAT CAT BAT DOG CAT DOG BAT BAT DOG CAT BAT CAT DOG ## m4 A peculiarity of this implementation is my use of arithmetic rather than branching to compute Sedgewick’s ‘k’. (I use arithmetic similarly in my Ratfor 77 implementation.) divert(-1) # 1-based indexing of a string's characters. define(get',substr($1',decr($2'),1)') define(set',substr($1',0,decr($2'))'$3'substr($1',$2')')
define(swap',
pushdef(_u',get($1',$2')')'dnl
pushdef(_v',get($1',$3')')'dnl
set(set($1',$2',_v),$3',_u)'dnl popdef(_u',_v')') #$1-fold repetition of $2. define(repeat',ifelse($1,0,',$2'$0(decr($1),$2')')')

#
# Heap's algorithm. Algorithm 2 in Robert Sedgewick, 1977. Permutation
# generation methods. ACM Comput. Surv. 9, 2 (June 1977), 137-164.
#
# This implementation permutes the characters in a string of length no
# more than 9. On longer strings, it may strain the resources of a
# very old implementation of m4.
#
define(permutations',
ifelse($2,',$1
$0($1',repeat(len($1'),1),2)', ifelse(eval(($3) <= len($1')),1, ifelse(eval(get($2,$3) <$3),1,
swap($1',_$0($2,$3),$3)$0(swap($1',_$0($2,$3),$3),set($2,$3,incr(get($2,$3))),2)', $0($1',set($2,$3,1),incr($3))')')')')
define(_permutations',eval((($2) % 2) + ((1 - (($2) % 2)) * get($1,$2)))')

divert'dnl
permutations(123')
permutations(abcd')
Output:

$m4 permutations.m4 123 213 312 132 231 321 abcd bacd cabd acbd bcad cbad dbac bdac adbc dabc badc abdc acdb cadb dacb adcb cdab dcab dcba cdba bdca dbca cbda bcda ## Maple combinat:-permute(3); [[1, 2, 3], [1, 3, 2], [2, 1, 3], [2, 3, 1], [3, 1, 2], [3, 2, 1]] combinat:-permute([a,b,c]); [[a, b, c], [a, c, b], [b, a, c], [b, c, a], [c, a, b], [c, b, a]] An implementation based on Mathematica solution: fold:=(f,a,v)->if(nops(v)=0,a,fold(f,f(a,op(1,v)),[op(2...,v)])): insert:=(v,a,n)->if(n>nops(v),[op(v),a],subsop(n=(a,v[n]),v)): perm:=s->fold((a,b)->map(u->seq(insert(u,b,k+1),k=0..nops(u)),a),[[]],s): perm([$1..3]);
[[3, 2, 1], [2, 3, 1], [2, 1, 3], [3, 1, 2], [1, 3, 2], [1, 2, 3]]

## Mathematica/Wolfram Language

Note: The built-in version will have better performance.

### Version from scratch

(***Standard list functions:*)
fold[f_, x_, {}] := x
fold[f_, x_, {h_, t___}] := fold[f, f[x, h], {t}]
insert[L_, x_, n_] := Join[L[[;; n - 1]], {x}, L[[n ;;]]]

(***Generate all permutations of a list S:*)

permutations[S_] :=
fold[Join @@ (Function[{L},
Table[insert[L, #2, k + 1], {k, 0, Length[L]}]] /@ #1) &, {{}},
S]

Output:
{{4, 3, 2, 1}, {3, 4, 2, 1}, {3, 2, 4, 1}, {3, 2, 1, 4}, {4, 2, 3,
1}, {2, 4, 3, 1}, {2, 3, 4, 1}, {2, 3, 1, 4}, {4, 2, 1, 3}, {2, 4,
1, 3}, {2, 1, 4, 3}, {2, 1, 3, 4}, {4, 3, 1, 2}, {3, 4, 1, 2}, {3,
1, 4, 2}, {3, 1, 2, 4}, {4, 1, 3, 2}, {1, 4, 3, 2}, {1, 3, 4,
2}, {1, 3, 2, 4}, {4, 1, 2, 3}, {1, 4, 2, 3}, {1, 2, 4, 3}, {1, 2,
3, 4}}

### Built-in version

Permutations[{1,2,3,4}]
Output:
{{1, 2, 3, 4}, {1, 2, 4, 3}, {1, 3, 2, 4}, {1, 3, 4, 2}, {1, 4, 2, 3}, {1, 4, 3, 2}, {2, 1, 3, 4}, {2, 1, 4, 3}, {2, 3, 1, 4}, {2, 3,
4, 1}, {2, 4, 1, 3}, {2, 4, 3, 1}, {3, 1, 2, 4}, {3, 1, 4, 2}, {3, 2, 1, 4}, {3, 2, 4, 1}, {3, 4, 1, 2}, {3, 4, 2, 1}, {4, 1, 2,
3}, {4, 1, 3, 2}, {4, 2, 1, 3}, {4, 2, 3, 1}, {4, 3, 1, 2}, {4, 3, 2, 1}}

perms([1,2,3,4])
Output:
4321
4312
4231
4213
4123
4132
3421
3412
3241
3214
3124
3142
2341
2314
2431
2413
2143
2134
1324
1342
1234
1243
1423
1432

## Maxima

next_permutation(v) := block([n, i, j, k, t],
n: length(v), i: 0,
for k: n - 1 thru 1 step -1 do (if v[k] < v[k + 1] then (i: k, return())),
j: i + 1, k: n,
while j < k do (t: v[j], v[j]: v[k], v[k]: t, j: j + 1, k: k - 1),
if i = 0 then return(false),
j: i + 1,
while v[j] < v[i] do j: j + 1,
t: v[j], v[j]: v[i], v[i]: t,
true
)$print_perm(n) := block([v: makelist(i, i, 1, n)], disp(v), while next_permutation(v) do disp(v) )$

print_perm(3);
/* [1, 2, 3]
[1, 3, 2]
[2, 1, 3]
[2, 3, 1]
[3, 1, 2]
[3, 2, 1] */

### Builtin version

(%i1) permutations([1, 2, 3]);
(%o1) {[1, 2, 3], [1, 3, 2], [2, 1, 3], [2, 3, 1], [3, 1, 2], [3, 2, 1]}

## Mercury

:- module permutations2.
:- interface.

:- import_module io.

:- pred main(io::di, io::uo) is det.

:- import_module list.
:- import_module set_ordlist.
:- import_module set.
:- import_module solutions.

%% permutationSet(List, Set) is true if List is a permutation of Set:
:- pred permutationSet(list(A)::out,set(A)::in) is nondet.

%% Two ways to compute all permutations of a given list (using backtracking):
:- func all_permutations1(list(int))=set_ordlist.set_ordlist(list(int)).
:- func all_permutations2(list(int))=set_ordlist.set_ordlist(list(int)).

:- implementation.

permutationSet([],set.init).
permutationSet([H|T], S) :- set.member(H,S), permutationSet(T,set.delete(S,H)).

all_permutations1(L) =
solutions_set(pred(X::out) is nondet:-permutationSet(X,set.from_list(L))).

%%Alternatively, using the imported list.perm predicate:
all_permutations2(L) =
solutions_set(pred(X::out) is nondet:-perm(L,X)).

main(!IO) :-
print(all_permutations1([1,2,3,4]),!IO),
nl(!IO),
print(all_permutations2([1,2,3,4]),!IO).

Output:
>./permutations2

sol([[1, 2, 3, 4], [1, 2, 4, 3], [1, 3, 2, 4], [1, 3, 4, 2], [1, 4, 2, 3], [1, 4, 3, 2], [2, 1, 3, 4], [2, 1, 4, 3], [2, 3, 1, 4], [2, 3, 4, 1], [2, 4, 1, 3], [2, 4, 3, 1], [3, 1, 2, 4], [3, 1, 4, 2], [3, 2, 1, 4], [3, 2, 4, 1], [3, 4, 1, 2], [3, 4, 2, 1], [4, 1, 2, 3], [4, 1, 3, 2], [4, 2, 1, 3], [4, 2, 3, 1], [4, 3, 1, 2], [4, 3, 2, 1]])
sol([[1, 2, 3, 4], [1, 2, 4, 3], [1, 3, 2, 4], [1, 3, 4, 2], [1, 4, 2, 3], [1, 4, 3, 2], [2, 1, 3, 4], [2, 1, 4, 3], [2, 3, 1, 4], [2, 3, 4, 1], [2, 4, 1, 3], [2, 4, 3, 1], [3, 1, 2, 4], [3, 1, 4, 2], [3, 2, 1, 4], [3, 2, 4, 1], [3, 4, 1, 2], [3, 4, 2, 1], [4, 1, 2, 3], [4, 1, 3, 2], [4, 2, 1, 3], [4, 2, 3, 1], [4, 3, 1, 2], [4, 3, 2, 1]])

## Microsoft Small Basic

Translation of: vba
'Permutations - sb
n=4
printem = "True"
For i = 1 To n
p[i] = i
EndFor
count = 0
Last = "False"
While Last = "False"
If printem Then
For t = 1 To n
TextWindow.Write(p[t])
EndFor
TextWindow.WriteLine("")
EndIf
count = count + 1
Last = "True"
i = n - 1
While i > 0
If p[i] < p[i + 1] Then
Last = "False"
Goto exitwhile
EndIf
i = i - 1
EndWhile
exitwhile:
j = i + 1
k = n
While j < k
t = p[j]
p[j] = p[k]
p[k] = t
j = j + 1
k = k - 1
EndWhile
j = n
While p[j] > p[i]
j = j - 1
EndWhile
j = j + 1
t = p[i]
p[i] = p[j]
p[j] = t
EndWhile
TextWindow.WriteLine("Number of permutations: "+count)
Output:
1234
1243
1324
1342
1423
1432
2134
2143
2314
2341
2413
2431
3124
3142
3214
3241
3412
3421
4123
4132
4213
4231
4312
4321
Number of permutations: 24

## Modula-2

MODULE 	Permute;

FROM Terminal

FROM Terminal2
IMPORT WriteString;

CONST MAXIDX = 6;
MINIDX = 1;

TYPE TInpCh = ['a'..'z'];
TChr = SET OF TInpCh;

VAR n,
nl: INTEGER;
ch: CHAR;
a: ARRAY[MINIDX..MAXIDX] OF CHAR;
kt: TChr = TChr{'a'..'f'};

PROCEDURE output;
VAR i: INTEGER;
BEGIN
FOR i := MINIDX TO n DO Write(a[i]) END;
WriteString(" | ");
END output;

PROCEDURE exchange(VAR x, y : CHAR);
VAR z: CHAR;
BEGIN z := x; x := y; y := z
END exchange;

PROCEDURE permute(k: INTEGER);
VAR i: INTEGER;
BEGIN
IF k = 1 THEN
output;
INC(nl);
IF (nl MOD 8 = 1) THEN WriteLn END;
ELSE
permute(k-1);
FOR i := MINIDX TO k-1 DO
exchange(a[i], a[k]);
permute(k-1);
exchange(a[i], a[k]);
END
END
END permute;

BEGIN
n := 0; nl := 1; WriteString("Input {a,b,c,d,e,f} >");
REPEAT
IF ch IN kt THEN INC(n); a[n] := ch; Write(ch) END
UNTIL (ch <= " ") OR (n > MAXIDX);

WriteLn;
IF n > 0 THEN permute(n) END;
(*Wait*)
END Permute.

## Modula-3

### Simple version

This implementation merely prints out the orbit of the list (1, 2, ..., n) under the action of Sn. It shows off Modula-3's built-in Set type and uses the standard IntSeq library module.

MODULE Permutations EXPORTS Main;

IMPORT IO, IntSeq;

CONST n = 3;

TYPE Domain = SET OF [ 1.. n ];

VAR

chosen: IntSeq.T;
values := Domain { };

PROCEDURE GeneratePermutations(VAR chosen: IntSeq.T; remaining: Domain) =
(*
Recursively generates all the permutations of elements
in the union of "chosen" and "values".
Values in "chosen" have already been chosen;
values in "remaining" can still be chosen.
If "remaining" is empty, it prints the sequence and returns.
Otherwise, it picks each element in "remaining", removes it,
adds it to "chosen", recursively calls itself,
then removes the last element of "chosen" and adds it back to "remaining".
*)

BEGIN
FOR i := 1 TO n DO
(* check if each element is in "remaining" *)
IF i IN remaining THEN
(* if so, remove from "remaining" and add to "chosen" *)
remaining := remaining - Domain { i };
IF remaining # Domain { } THEN
(* still something to process? do it *)
GeneratePermutations(chosen, remaining);
ELSE
(* otherwise, print what we've chosen *)
FOR j := 0 TO chosen.size() - 2 DO
IO.PutInt(chosen.get(j)); IO.Put(", ");
END;
IO.PutInt(chosen.gethi());
IO.PutChar('\n');
END;
(* add "i" back to "remaining" and remove from "chosen" *)
remaining := remaining + Domain { i };
EVAL chosen.remhi();
END;
END;
END GeneratePermutations;

BEGIN

(* initial setup *)
chosen := NEW(IntSeq.T).init(n);
FOR i := 1 TO n DO values := values + Domain { i }; END;

GeneratePermutations(chosen, values);

END Permutations.
Output:

For reasons of space, we show only the elements of S3, but we have tested it with higher.

1, 2, 3
1, 3, 2
2, 1, 3
2, 3, 1
3, 1, 2
3, 2, 1

### Generic version

This version works on any type, and requires the library's Set and Sequence. As usual in Modula-3, the generic instance will need to be instantiated for whatever type you want to use, and you will also need to instantiate a set of, sequence of, and sequence of sequences of the domain elements. This will have to be taken care of by the m3makefile.

interface

Suppose that D is the domain of elements to be permuted. This module requires a DomainSeq (Sequence of D), a DomainSet (Set of D), and a DomainSeqSeq (Sequence of Sequences of Domain).

GENERIC INTERFACE GenericPermutations(DomainSeq, DomainSet, DomainSeqSeq);

(*
"Domain" is where the things to permute come from (unused in interface).
"DomainSeq" is a "Sequence" of "Domain".
"DomainSet" is a "Set" of "Domain".
"DomainSeqSeq" is a "Sequence" of "DomainSeq".
*)

PROCEDURE GeneratePermutations(
);
(*
Recursively generates all the permutations of elements
in the union of "chosen" and "remaining".
Values in "chosen" have already been chosen;
values in "remaining" can still be chosen.
If "remaining" is empty, it adds the permutation to "result".
Otherwise, it picks each element in "remaining", removes it,
adds it to "chosen", recursively calls itself,
then removes the last element of "chosen" and adds it back to "remaining".
Although the parameters are modified, we can describe them as "READONLY"
because we do not re-assign them.
*)

END GenericPermutations.
implementation

In addition to the interface's specifications, this requires a generic Domain. Some implementations of a set are not safe to iterate over while modifying (e.g., a tree), so this copies the values and iterates over them.

GENERIC MODULE GenericPermutations(Domain, DomainSeq, DomainSet, DomainSeqSeq);

(*
"Domain" is where the things to permute come from.
"DomainSeq" is a "Sequence" of "Domain".
"DomainSet" is a "Set" of "Domain".
"DomainSeqSeq" is a "Sequence" of "DomainSeq".
*)

PROCEDURE GeneratePermutations(
) =

(*
Recursively generates all the permutations of elements
in the union of "chosen" and "remaining".
Values in "chosen" have already been chosen;
values in "remaining" can still be chosen.
If "remaining" is empty, it adds the permutation to "result".
Otherwise, it picks each element in "remaining", removes it,
adds it to "chosen", recursively calls itself,
then removes the last element of "chosen" and adds it back to "remaining".
*)

VAR

r: Domain.T; (* element added to permutation *)

iterator := remaining.iterate(); (* to iterate through remaining elements *)

values := NEW(DomainSeq.T).init(remaining.size());
(* used to store values for iteration *)

BEGIN

(* cannot safely modify a set while iterating, so we'll store the values *)

(* now loop through the stored values *)
FOR i := 0 TO values.size() - 1 DO

(* remove from "remaining" and add to "chosen" *)
r := values.get(i);
EVAL remaining.delete(r);

(* if this is not the last remaining elements, call recursively *)
IF remaining.size() # 0 THEN
GeneratePermutations(chosen, remaining, result);
ELSE
(* we have a new permutation; add a copy to the set *)
VAR newPerm := NEW(DomainSeq.T).init(chosen.size());
BEGIN
FOR i := 0 TO chosen.size() - 1 DO
END;
END;
END;

(* move r back from chosen *)
EVAL remaining.insert(chosen.remhi());

END;

END GeneratePermutations;

BEGIN
END GenericPermutations.
Sample Usage

Here the domain is Integer, but the interface doesn't require that, so we "merely" need IntSeq (a Sequence of Integer), IntSetTree (a set type I use, but you could use SetDef or SetList if you prefer; I've tested it and it works), IntSeqSeq (a Sequence of Sequences of Integer), and IntPermutations, which is GenericPermutations instantiated for Integer.

MODULE GPermutations EXPORTS Main;

IMPORT IO, IntSeq, IntSetTree, IntSeqSeq, IntPermutations;

CONST

n = 7;

VAR

chosen: IntSeq.T;
remaining: IntSetTree.T;
result: IntSeqSeq.T;

PROCEDURE Factorial(n: CARDINAL): CARDINAL =
VAR result := 1;
BEGIN
FOR i := 2 TO n DO
result := result * i;
END;
RETURN result;
END Factorial;

BEGIN

(* initial setup *)
chosen := NEW(IntSeq.T).init(n);
remaining := NEW(IntSetTree.T).init();
result := NEW(IntSeqSeq.T).init(Factorial(n));
FOR i := 1 TO n DO EVAL remaining.insert(i); END;

IntPermutations.GeneratePermutations(chosen, remaining, result);

IO.Put("Printing "); IO.PutInt(result.size());
IO.Put(" permutations of "); IO.PutInt(n); IO.Put(" elements \n");
FOR i := 0 TO result.size() - 1 DO
FOR j := 0 TO result.get(i).size() - 1 DO
IO.PutInt(result.get(i).get(j)); IO.PutChar(' ');
END;
IO.PutChar('\n');
END;

END GPermutations.
Output:
(somewhat edited!)
Printing 5040 permutations of 7 elements
1 2 3 4 5 6 7
1 2 3 4 5 7 6
1 2 3 4 6 5 7
...
7 6 5 4 2 3 1
7 6 5 4 3 1 2
7 6 5 4 3 2 1

## NetRexx

/* NetRexx */
options replace format comments java crossref symbols nobinary

import java.util.List
import java.util.ArrayList

-- =============================================================================
/**
* Permutation Iterator
* <br />
* <br />
* Algorithm by E. W. Dijkstra, "A Discipline of Programming", Prentice-Hall, 1976, p.71
*/

class RPermutationIterator implements Iterator

-- ---------------------------------------------------------------------------
properties indirect
perms = List
permOrders = int[]
maxN
currentN
first = boolean

-- ---------------------------------------------------------------------------
properties constant
isTrue = boolean (1 == 1)
isFalse = boolean (1 \= 1)

-- ---------------------------------------------------------------------------
method RPermutationIterator(initial = List) public
setUp(initial)
return

-- ---------------------------------------------------------------------------
method RPermutationIterator(initial = Object[]) public
init = ArrayList(initial.length)
loop elmt over initial
end elmt
setUp(init)
return

-- ---------------------------------------------------------------------------
method RPermutationIterator(initial = Rexx[]) public
init = ArrayList(initial.length)
loop elmt over initial
end elmt
setUp(init)
return

-- ---------------------------------------------------------------------------
method setUp(initial = List) private
setFirst(isTrue)
setPerms(initial)
setPermOrders(int[getPerms().size()])
setMaxN(getPermOrders().length)
setCurrentN(0)
po = getPermOrders()
loop i_ = 0 while i_ < po.length
po[i_] = i_
end i_
return

-- ---------------------------------------------------------------------------
method hasNext() public returns boolean
status = isTrue
if getCurrentN() == factorial(getMaxN()) then status = isFalse
setCurrentN(getCurrentN() + 1)
return status

-- ---------------------------------------------------------------------------
method next() public returns Object
if isFirst() then setFirst(isFalse)
else do
po = getPermOrders()
i_ = getMaxN() - 1
loop while po[i_ - 1] >= po[i_]
i_ = i_ - 1
end

j_ = getMaxN()
loop while po[j_ - 1] <= po[i_ - 1]
j_ = j_ - 1
end

swap(i_ - 1, j_ - 1)

i_ = i_ + 1
j_ = getMaxN()
loop while i_ < j_
swap(i_ - 1, j_ - 1)
i_ = i_ + 1
j_ = j_ - 1
end
end
return reorder()

-- ---------------------------------------------------------------------------
method remove() public signals UnsupportedOperationException
signal UnsupportedOperationException()

-- ---------------------------------------------------------------------------
method swap(i_, j_) private
po = getPermOrders()
save = po[i_]
po[i_] = po[j_]
po[j_] = save
return

-- ---------------------------------------------------------------------------
method reorder() private returns List
result = ArrayList(getPerms().size())
loop ix over getPermOrders()
end ix
return result

-- ---------------------------------------------------------------------------
/**
* Calculate n factorial: {@code n! = 1 * 2 * 3 .. * n}
* @param n
* @return n!
*/

method factorial(n) public static
fact = 1
if n > 1 then loop i = 1 while i <= n
fact = fact * i
end i
return fact

-- ---------------------------------------------------------------------------
method main(args = String[]) public static
thing02 = RPermutationIterator(['alpha', 'omega'])
thing03 = RPermutationIterator([String 'one', 'two', 'three'])
thing04 = RPermutationIterator(Arrays.asList([Integer(1), Integer(2), Integer(3), Integer(4)]))
things = [thing02, thing03, thing04]
loop thing over things
N = thing.getMaxN()
say 'Permutations:' N'! =' factorial(N)
loop lineCount = 1 while thing.hasNext()
prm = thing.next()
say lineCount.right(8)':' prm.toString()
end lineCount
say 'Permutations:' N'! =' factorial(N)
say
end thing
return

Output:
Permutations: 2! = 2
1: [alpha, omega]
2: [omega, alpha]
Permutations: 2! = 2

Permutations: 3! = 6
1: [one, two, three]
2: [one, three, two]
3: [two, one, three]
4: [two, three, one]
5: [three, one, two]
6: [three, two, one]
Permutations: 3! = 6

Permutations: 4! = 24
1: [1, 2, 3, 4]
2: [1, 2, 4, 3]
3: [1, 3, 2, 4]
4: [1, 3, 4, 2]
5: [1, 4, 2, 3]
6: [1, 4, 3, 2]
7: [2, 1, 3, 4]
8: [2, 1, 4, 3]
9: [2, 3, 1, 4]
10: [2, 3, 4, 1]
11: [2, 4, 1, 3]
12: [2, 4, 3, 1]
13: [3, 1, 2, 4]
14: [3, 1, 4, 2]
15: [3, 2, 1, 4]
16: [3, 2, 4, 1]
17: [3, 4, 1, 2]
18: [3, 4, 2, 1]
19: [4, 1, 2, 3]
20: [4, 1, 3, 2]
21: [4, 2, 1, 3]
22: [4, 2, 3, 1]
23: [4, 3, 1, 2]
24: [4, 3, 2, 1]
Permutations: 4! = 24

## Nim

### Using the standard library

import algorithm
var v = [1, 2, 3] # List has to start sorted
echo v
while v.nextPermutation():
echo v
Output:
[1, 2, 3]
[1, 3, 2]
[2, 1, 3]
[2, 3, 1]
[3, 1, 2]
[3, 2, 1]

### Single yield iterator

iterator inplacePermutations[T](xs: var seq[T]): var seq[T] =
assert xs.len <= 24, "permutation of array longer than 24 is not supported"

let n = xs.len - 1
var
c: array[24, int8]
i: int = 0

for i in 0 .. n: c[i] = int8(i+1)

while true:
yield xs
if i >= n: break

c[i] -= 1
let j = if (i and 1) == 1: 0 else: int(c[i])
swap(xs[i+1], xs[j])

i = 0
while c[i] == 0:
let t = i+1
c[i] = int8(t)
i = t

verification

import intsets
from math import fac
block:
# test all permutations of length from 0 to 9
for l in 0..9:

# prepare data
var xs = newSeq[int](l)
for i in 0..<l: xs[i] = i
var s = initIntSet()

for cs in inplacePermutations(xs):

# each permutation must be of length l
assert len(cs) == l

# each permutation must contain digits from 0 to l-1 exactly once
var ds = newSeq[bool](l)
for c in cs:
assert not ds[c]
ds[c] = true

# generate a unique number for each permutation
var h = 0
for e in cs:
h = l * h + e
assert not s.contains(h)
s.incl(h)

# check exactly l! unique number of permutations
assert len(s) == fac(l)

### Translation of C

Translation of: C
# iterative Boothroyd method
iterator permutations[T](ys: openarray[T]): seq[T] =
var
d = 1
c = newSeq[int](ys.len)
xs = newSeq[T](ys.len)

for i, y in ys: xs[i] = y
yield xs

block outer:
while true:
while d > 1:
dec d
c[d] = 0
while c[d] >= d:
inc d
if d >= ys.len: break outer
let i = if (d and 1) == 1: c[d] else: 0
swap xs[i], xs[d]
yield xs
inc c[d]

var x = @[1,2,3]

for i in permutations(x):
echo i

Output:

@[1, 2, 3]
@[2, 1, 3]
@[3, 1, 2]
@[1, 3, 2]
@[2, 3, 1]
@[3, 2, 1]

### Translation of Go

Translation of: Go
# Nim implementation of the (very fast) Go example.
# http://rosettacode.org/wiki/Permutations#Go
# implementing a recursive https://en.wikipedia.org/wiki/Steinhaus–Johnson–Trotter_algorithm

import algorithm

proc perm(s: openArray[int]; emit: proc(emit: openArray[int])) =
var s = @s
if s.len == 0:
emit(s)
return

proc rc(np: int) =
if np == 1:
emit(s)
return
var
np1 = np - 1
pp = s.len - np1

rc(np1) # Recurse prior swaps.

for i in countDown(pp, 1):
swap s[i], s[i-1]
rc(np1) # Recurse swap.

s.rotateLeft(0..pp, 1)

rc(s.len)

var se = @[0, 1, 2, 3] #, 4, 5, 6, 7, 8, 9, 10]

perm(se, proc(s: openArray[int])= echo s)

## OCaml

(* Iterative, though loops are implemented as auxiliary recursive functions.

let next_perm p =
let n = Array.length p in
let i = let rec aux i =
if (i < 0) || (p.(i) < p.(i+1)) then i
else aux (i - 1) in aux (n - 2) in
let rec aux j k = if j < k then
let t = p.(j) in
p.(j) <- p.(k);
p.(k) <- t;
aux (j + 1) (k - 1)
else () in aux (i + 1) (n - 1);
if i < 0 then false else
let j = let rec aux j =
if p.(j) > p.(i) then j
else aux (j + 1) in aux (i + 1) in
let t = p.(i) in
p.(i) <- p.(j);
p.(j) <- t;
true;;

let print_perm p =
let n = Array.length p in
for i = 0 to n - 2 do
print_int p.(i);
print_string " "
done;
print_int p.(n - 1);
print_newline ();;

let print_all_perm n =
let p = Array.init n (function i -> i + 1) in
print_perm p;
while next_perm p do
print_perm p
done;;

print_all_perm 3;;
(* 1 2 3
1 3 2
2 1 3
2 3 1
3 1 2
3 2 1 *)

Permutations can also be defined on lists recursively:

let rec permutations l =
let n = List.length l in
if n = 1 then [l] else
let rec sub e = function
| [] -> failwith "sub"
| h :: t -> if h = e then t else h :: sub e t in
let rec aux k =
let e = List.nth l k in
let subperms = permutations (sub e l) in
let t = List.map (fun a -> e::a) subperms in
if k < n-1 then List.rev_append t (aux (k+1)) else t in
aux 0;;

let print l = List.iter (Printf.printf " %d") l; print_newline() in
List.iter print (permutations [1;2;3;4])

or permutations indexed independently:

let rec pr_perm k n l =
let a, b = let c = k/n in c, k-(n*c) in
let e = List.nth l b in
let rec sub e = function
| [] -> failwith "sub"
| h :: t -> if h = e then t else h :: sub e t in
(Printf.printf " %d" e; if n > 1 then pr_perm a (n-1) (sub e l))

let show_perms l =
let n = List.length l in
let rec fact n = if n < 3 then n else n * fact (n-1) in
for i = 0 to (fact n)-1 do
pr_perm i n l;
print_newline()
done

let () = show_perms [1;2;3;4]

## ooRexx

Essentially derived fom the program shown under rexx. This program works also with Regina (and other REXX implementations?)

/* REXX Compute bunch permutations of things elements */
Parse Arg bunch things
If bunch='?' Then
Call help
If bunch=='' Then bunch=3
If datatype(bunch)<>'NUM' Then Call help 'bunch ('bunch') must be numeric'
thing.=''
Select
When things='' Then things=bunch
When datatype(things)='NUM' Then Nop
Otherwise Do
data=things
things=words(things)
Do i=1 To things
Parse Var data thing.i data
End
End
End
If things<bunch Then Call help 'things ('things') must be >= bunch ('bunch')'

perms =0
Call time 'R'
Call permSets things, bunch
Say perms 'Permutations'
Say time('E') 'seconds'
Exit

/*--------------------------------------------------------------------------------------*/
first_word: return word(Arg(1),1)
/*--------------------------------------------------------------------------------------*/
permSets: Procedure Expose perms thing.
Parse Arg things,bunch
aa.=''
sep=''
perm_elements='123456789ABCDEF'
Do k=1 To things
perm=first_word(first_word(substr(perm_elements,k,1) k))
dd.k=perm
End
Call .permSet 1
Return

.permSet: Procedure Expose dd. aa. things bunch perms thing.
Parse Arg iteration
If iteration>bunch Then do
perm= aa.1
Do j=2 For bunch-1
perm= perm aa.j
End
perms+=1
If thing.1<>'' Then Do
ol=''
Do pi=1 To words(perm)
z=word(perm,pi)
If datatype(z)<>'NUM' Then
z=9+pos(z,'ABCDEF')
ol=ol thing.z
End
Say strip(ol)
End
Else
Say perm
End
Else Do
Do q=1 for things
Do k=1 for iteration-1
If aa.k==dd.q Then
iterate q
End
aa.iteration= dd.q
Call .permSet iteration+1
End
End
Return

help:
Parse Arg msg
If msg<>'' Then Do
Say 'ERROR:' msg
Say ''
End
Say 'rexx perm -> Permutations of 1 2 3 '
Say 'rexx perm 2 -> Permutations of 1 2 '
Say 'rexx perm 2 4 -> Permutations of 1 2 3 4 in 2 positions'
Say 'rexx perm 2 a b c d -> Permutations of a b c d in 2 positions'
Exit
Output:
H:\>rexx perm 2 U V W X
U V
U W
U X
V U
V W
V X
W U
W V
W X
X U
X V
X W
12 Permutations
0.006000 seconds

H:\>rexx perm ?
rexx perm            -> Permutations of 1 2 3
rexx perm 2          -> Permutations of 1 2
rexx perm 2 4        -> Permutations of 1 2 3 4 in 2 positions
rexx perm 2 a b c d  -> Permutations of a b c d in 2 positions

## OpenEdge/Progress

DEFINE VARIABLE charArray AS CHARACTER EXTENT 3 INITIAL ["A","B","C"].
DEFINE VARIABLE sizeofArray AS INTEGER.

sizeOfArray = EXTENT(charArray).

RUN GetPermutations(1).

PROCEDURE GetPermutations:
DEFINE INPUT PARAMETER n AS INTEGER.

DEFINE VARIABLE i AS INTEGER.
DEFINE VARIABLE j AS INTEGER.
DEFINE VARIABLE currentPermutation AS CHARACTER.

REPEAT i = n TO sizeOfArray:
RUN swapValues(i,n).
RUN GetPermutations(n + 1).
RUN swapValues(i,n).
END.
IF n = sizeOfArray THEN DO:
DO j = 1 TO EXTENT(charArray):
currentPermutation = currentPermutation + charArray[j].
END.
DISPLAY currentPermutation WITH FRAME A DOWN.
END.
END PROCEDURE.

PROCEDURE swapValues:
DEFINE INPUT PARAMETER a AS INTEGER.
DEFINE INPUT PARAMETER b AS INTEGER.
DEFINE VARIABLE temp AS CHARACTER.
temp = charArray[a].
charArray[a] = charArray[b].
charArray[b] = temp.
END PROCEDURE.
Output:
ABC
ACB
BAC
BCA
CAB
CBA

## PARI/GP

vector(n!,k,numtoperm(n,k))

## Pascal

program perm;

var
p: array[1 .. 12] of integer;
is_last: boolean;
n: integer;

procedure next;
var i, j, k, t: integer;
begin
is_last := true;
i := n - 1;
while i > 0 do
begin
if p[i] < p[i + 1] then
begin
is_last := false;
break;
end;
i := i - 1;
end;

if not is_last then
begin
j := i + 1;
k := n;
while j < k do
begin
t := p[j];
p[j] := p[k];
p[k] := t;
j := j + 1;
k := k - 1;
end;

j := n;
while p[j] > p[i] do j := j - 1;
j := j + 1;

t := p[i];
p[i] := p[j];
p[j] := t;
end;
end;

procedure print;
var i: integer;
begin
for i := 1 to n do write(p[i], ' ');
writeln;
end;

procedure init;
var i: integer;
begin
n := 0;
while (n < 1) or (n > 10) do
begin
write('Enter n (1 <= n <= 10): ');
end;
for i := 1 to n do p[i] := i;
end;

begin
init;
repeat
print;
next;
until is_last;
end.

### alternative

a little bit more speed.I take n = 12. The above version takes more than 5 secs.My permlex takes 2.8s, but in the depth of my harddisk I found a version, creating all permutations using k places out of n.The cpu loves it! 1.33 s. But you have to use the integers [1..n] directly or as Index to your data. 1 to n are in lexicographic order.

{$IFDEF FPC} {$MODE DELPHI}
{$ELSE} {$APPTYPE CONSOLE}
{$ENDIF} uses sysutils; type tPermfield = array[0..15] of Nativeint; var permcnt: NativeUint; procedure DoSomething(k: NativeInt;var x:tPermfield); var i:integer; kk:string; begin kk:=''; for i:=1 to k do kk:=kk+inttostr(x[i])+' '; writeln(kk); end; procedure PermKoutOfN(k,n: nativeInt); var x,y:tPermfield; i,yi,tmp:NativeInt; begin //initialise permcnt:= 1; if k>n then k:=n; if k=n then k:=k-1; for i:=1 to n do x[i]:=i; for i:=1 to k do y[i]:=i; // DoSomething(k,x); i := k; repeat yi:=y[i]; if yi <n then begin inc(permcnt); inc(yi); y[i]:=yi; tmp:=x[i];x[i]:=x[yi];x[yi]:=tmp; i:=k; // DoSomething(k,x); end else begin repeat tmp:=x[i];x[i]:=x[yi];x[yi]:=tmp; dec(yi); until yi<=i; y[i]:=yi; dec(i); end; until (i=0); end; var t1,t0 : TDateTime; Begin permcnt:= 0; T0 := now; PermKoutOfN(12,12); T1 := now; writeln(permcnt); writeln(FormatDateTime('HH:NN:SS.zzz',T1-T0)); end. Output: {fpc 2.64/3.0 32Bit or 3.1 64 Bit i4330 3.5 Ghz same timings. //PermKoutOfN(12,12); 479001600 //= 12! 00:00:01.328 ### Permutations from integers A console application in Free Pascal, created with the Lazarus IDE. program Permutations; (* Demonstrates four closely related ways of establishing a bijection between permutations of 0..(n-1) and integers 0..(n! - 1). Each integer in that range is represented by mixed-base digits d[0..n-1], where each d[j] satisfies 0 <= d[j] <=j. The integer represented by d[0..n-1] is d[n-1]*(n-1)! + d[n-2]*(n-2)! + ... + d[1]*1! + d[0]*0! where the last term can be omitted in practice because d[0] is always 0. See the section "Numbering permutations" in the Wikipedia article "Permutation" (NB their digit array d is 1-based). *) uses SysUtils, TypInfo; type TPermIntMapping = (map_I, map_J, map_K, map_L); type TPermutation = array of integer; // Function to map an integer to a permutation. function IntToPerm( map : TPermIntMapping; nrItems, z : integer) : TPermutation; var d, lookup : array of integer; x, y : integer; h, j, k, m : integer; begin SetLength( result, nrItems); SetLength( lookup, nrItems); SetLength( d, nrItems); m := nrItems - 1; // Convert z to digits d[0..m] (see comment at head of program). d[0] := 0; y := z; for j := 1 to m - 1 do begin x := y div (j + 1); d[j] := y - x*(j + 1); y := x; end; d[m] := y; // Set up the permutation elements case map of map_I, map_L: for j := 0 to m do lookup[j] := j; map_J, map_K: for j := 0 to m do lookup[j] := m - j; end; for j := m downto 0 do begin k := d[j]; case map of map_I: result[lookup[k]] := m - j; map_J: result[j] := lookup[k]; map_K: result[lookup[k]] := j; map_L: result[m - j] := lookup[k]; end; // When lookup[k] has been used, it's removed from the lookup table // and the elements above it are moved down one place. for h := k to j - 1 do lookup[h] := lookup[h + 1]; end; end; // Function to map a permutation to an integer; inverse of the above. // Put in for completeness, not required for Rosetta Code task. function PermToInt( map : TPermIntMapping; p : TPermutation) : integer; var m, i, j, k : integer; d : array of integer; begin m := High(p); // number of items in permutation is m + 1 SetLength( d, m + 1); for k := 0 to m do d[k] := 0; // initialize all digits to 0 // Looking for inversions for i := 0 to m - 1 do begin for j := i + 1 to m do begin if p[j] < p[i] then begin case map of map_I : inc( d[m - p[j]]); map_J : inc( d[j]); map_K : inc( d[p[i]]); map_L : inc( d[m - i]); end; end; end; end; // Get result from its digits (see comment at head of program). result := d[m]; for j := m downto 2 do result := result*j + d[j - 1]; end; // Main routine to generate permutations of the integers 0..(n-1), // where n is passed as a command-line parameter, e.g. Permutations 4 var n, n_fac, z, j : integer; nrErrors : integer; perm : TPermutation; map : TPermIntMapping; lineOut : string; pinfo : TypInfo.PTypeInfo; begin n := SysUtils.StrToInt( ParamStr(1)); n_fac := 1; for j := 2 to n do n_fac := n_fac*j; pinfo := System.TypeInfo( TPermIntMapping); lineOut := 'integer'; for map := Low( TPermIntMapping) to High( TPermIntMapping) do begin lineOut := lineOut + ' ' + TypInfo.GetEnumName( pinfo, ord(map)); end; WriteLn( lineOut); for z := 0 to n_fac - 1 do begin lineOut := SysUtils.Format( '%7d', [z]); for map := Low( TPermIntMapping) to High( TPermIntMapping) do begin perm := IntToPerm( map, n, z); // Check the inverse mapping (not required for Rosetta Code task) Assert( z = PermToInt( map, perm)); lineOut := lineOut + ' '; for j := 0 to n - 1 do lineOut := lineOut + SysUtils.Format( '%d', [perm[j]]); end; WriteLn( lineOut); end; end. Output: integer map_I map_J map_K map_L 0 0123 0123 0123 0123 1 0132 1023 1023 0132 2 0213 0213 0213 0213 3 0312 2013 1203 0231 4 0231 1203 2013 0312 5 0321 2103 2103 0321 6 1023 0132 0132 1023 7 1032 1032 1032 1032 8 2013 0312 0231 1203 9 3012 3012 1230 1230 10 2031 1302 2031 1302 11 3021 3102 2130 1320 12 1203 0231 0312 2013 13 1302 2031 1302 2031 14 2103 0321 0321 2103 15 3102 3021 1320 2130 16 2301 2301 2301 2301 17 3201 3201 2310 2310 18 1230 1230 3012 3012 19 1320 2130 3102 3021 20 2130 1320 3021 3102 21 3120 3120 3120 3120 22 2310 2310 3201 3201 23 3210 3210 3210 3210 ## Perl A simple recursive implementation. sub permutation { my ($perm,@set) = @_;
print "$perm\n" || return unless (@set); permutation($perm.$set[$_],@set[0..$_-1],@set[$_+1..$#set]) foreach (0..$#set);
}
my @input = (qw/a b c d/);
permutation('',@input);
Output:
abcd
abdc
acbd
acdb
bacd
bcda
bdac
bdca
cabd
cbda
cdab
cdba
dabc
dacb
dbac
dbca
dcab
dcba

For better performance, use a module like ntheory or Algorithm::Permute.

Library: ntheory
use ntheory qw/forperm/;
my @tasks = (qw/party sleep study/);
forperm {
Output:
party sleep study
party study sleep
sleep party study
sleep study party
study party sleep
study sleep party

## Phix

with javascript_semantics
requires("1.0.2")
?shorten(permutes("abcd"),"elements",5)
Output:

The elements can be any type. There is also a permute() function which accepts an integer between 1 and factorial(length(s)) and returns the permutations in lexicographical position order. It is just as fast to generate the (n!)th permutation as the first, so some applications may benefit by storing an integer key rather than duplicating all the elements of the given set.

## Phixmonti

include ..\Utilitys.pmt

def save
over over chain ps> swap 0 put >ps
enddef

def permute /# l l -- #/
len 2 > if
len for drop
pop swap rot swap 1 put swap permute
endfor
else
save rotate save rotate
endif
swap len if
pop rot rot 0 put
else
drop drop
endif
enddef

( ) >ps
( ) ( 1 2 3 4 ) permute
ps> sort print

## Picat

Picat has built-in support for permutations:

• permutation(L): Generates all permutations for a list L.
• permutation(L,P): Generates (via backtracking) all permutations for a list L.

### Recursion

Use findall/2 to find all permutations. See example below.

permutation_rec1([X|Y],Z) :-
permutation_rec1(Y,W),
select(X,Z,W).
permutation_rec1([],[]).

permutation_rec2([], []).
permutation_rec2([X], [X]) :-!.
permutation_rec2([T|H], X) :-
permutation_rec2(H, H1),
append(L1, L2, H1),
append(L1, [T], X1),
append(X1, L2, X).

### Constraint modelling

Constraint modelling only handles integers, and here generates all permutations of a list 1..N for a given N.

permutation_cp_list(L) permutes a list via permutation_cp2/1.

import cp.

% Returns all permutations
permutation_cp1(N) = solve_all(X) =>
X = new_list(N),
X :: 1..N,
all_different(X).

% Find next permutation on backtracking
permutation_cp2(N,X) =>
X = new_list(N),
X :: 1..N,
all_different(X),
solve(X).

% Use the cp approach on a list L.
permutation_cp_list(L) = Perms =>
Perms = [ [L[I] : I in P] : P in permutation_cp1(L.len)].

### Tests

Here is a test of the different approaches, including the two built-ins.

import util, cp.
main =>
N = 3,
println(permutations=permutations(1..N)), % built in
println(permutation=findall(P,permutation([a,b,c],P))), % built-in
println(permutation_rec1=findall(P,permutation_rec1(1..N,P))),
println(permutation_rec2=findall(P,permutation_rec2(1..N,P))),
println(permutation_cp1=permutation_cp1(N)),
println(permutation_cp2=findall(P,permutation_cp2(N,P))),
println(permutation_cp_list=permutation_cp_list("abc")).
Output:
permutations = [[1,2,3],[2,1,3],[2,3,1],[1,3,2],[3,1,2],[3,2,1]]
permutation = [abc,acb,bac,bca,cab,cba]
permutation_rec1 = [[1,2,3],[2,1,3],[2,3,1],[1,3,2],[3,1,2],[3,2,1]]
permutation_rec2 = [[1,2,3],[2,1,3],[2,3,1],[1,3,2],[3,1,2],[3,2,1]]
permutation_cp1 = [[1,2,3],[1,3,2],[2,1,3],[2,3,1],[3,1,2],[3,2,1]]
permutation_cp2 = [[1,2,3],[1,3,2],[2,1,3],[2,3,1],[3,1,2],[3,2,1]]
permutation_cp_list = [abc,acb,bac,bca,cab,cba]

## PicoLisp

(permute (1 2 3))
Output:
-> ((1 2 3) (1 3 2) (2 1 3) (2 3 1) (3 1 2) (3 2 1))

## PowerBASIC

Works with: PowerBASIC version 10.00+
#COMPILE EXE
#DIM ALL
GLOBAL a, i, j, k, n AS INTEGER
GLOBAL d, ns, s AS STRING 'dynamic string
FUNCTION PBMAIN () AS LONG
ns = INPUTBOX$(" n =",, "3") 'input n n = VAL(ns) DIM a(1 TO n) AS INTEGER FOR i = 1 TO n: a(i)= i: NEXT DO s = " " FOR i = 1 TO n d = STR$(a(i))
s = BUILD$(s, d) ' s & d concatenate NEXT ? s 'print and pause i = n DO DECR i LOOP UNTIL i = 0 OR a(i) < a(i+1) j = i+1 k = n DO WHILE j < k SWAP a(j), a(k) INCR j DECR k LOOP IF i > 0 THEN j = i+1 DO WHILE a(j) < a(i) INCR j LOOP SWAP a(i), a(j) END IF LOOP UNTIL i = 0 END FUNCTION Output: 1 2 3 1 3 2 2 1 3 2 3 1 3 1 2 3 2 1 ## PowerShell function permutation ($array) {
function generate($n,$array, $A) { if($n -eq 1) {
$array[$A] -join ' '
}
else{
for( $i = 0;$i -lt ($n - 1);$i += 1) {
generate ($n - 1)$array $A if($n % 2 -eq 0){
$i1,$i2 = $i, ($n-1)
$A[$i1], $A[$i2] = $A[$i2], $A[$i1]
}
else{
$i1,$i2 = 0, ($n-1)$A[$i1],$A[$i2] =$A[$i2],$A[$i1] } } generate ($n - 1) $array$A
}
}
$n =$array.Count
if($n -gt 0) { (generate$n $array (0..($n-1)))
} else {$array} } permutation @('A','B','C') Output: A B C B A C C A B A C B B C A C B A ## Prolog Works with SWI-Prolog and library clpfd, :- use_module(library(clpfd)). permut_clpfd(L, N) :- length(L, N), L ins 1..N, all_different(L), label(L). Output: ?- permut_clpfd(L, 3), writeln(L), fail. [1,2,3] [1,3,2] [2,1,3] [2,3,1] [3,1,2] [3,2,1] false. A declarative way of fetching permutations: % permut_Prolog(P, L) % P is a permutation of L permut_Prolog([], []). permut_Prolog([H | T], NL) :- select(H, NL, NL1), permut_Prolog(T, NL1). Output: ?- permut_Prolog(P, [ab, cd, ef]), writeln(P), fail. [ab,cd,ef] [ab,ef,cd] [cd,ab,ef] [cd,ef,ab] [ef,ab,cd] [ef,cd,ab] false. Translation of: Curry insert(X, L, [X|L]). insert(X, [Y|Ys], [Y|L2]) :- insert(X, Ys, L2). permutation([], []). permutation([X|Xs], P) :- permutation(Xs, L), insert(X, L, P). Output: ?- permutation([a,b,c],X). X = [a, b, c] ; X = [b, a, c] ; X = [b, c, a] ; X = [a, c, b] ; X = [c, a, b] ; X = [c, b, a] ; false. ## PureBasic The procedure nextPermutation() takes an array of integers as input and transforms its contents into the next lexicographic permutation of it's elements (i.e. integers). It returns #True if this is possible. It returns #False if there are no more lexicographic permutations left and arranges the elements into the lowest lexicographic permutation. It also returns #False if there is less than 2 elemetns to permute. The integer elements could be the addresses of objects that are pointed at instead. In this case the addresses will be permuted without respect to what they are pointing to (i.e. strings, or structures) and the lexicographic order will be that of the addresses themselves. Macro reverse(firstIndex, lastIndex) first = firstIndex last = lastIndex While first < last Swap cur(first), cur(last) first + 1 last - 1 Wend EndMacro Procedure nextPermutation(Array cur(1)) Protected first, last, elementCount = ArraySize(cur()) If elementCount < 1 ProcedureReturn #False ;nothing to permute EndIf ;Find the lowest position pos such that [pos] < [pos+1] Protected pos = elementCount - 1 While cur(pos) >= cur(pos + 1) pos - 1 If pos < 0 reverse(0, elementCount) ProcedureReturn #False ;no higher lexicographic permutations left, return lowest one instead EndIf Wend ;Swap [pos] with the highest positional value that is larger than [pos] last = elementCount While cur(last) <= cur(pos) last - 1 Wend Swap cur(pos), cur(last) ;Reverse the order of the elements in the higher positions reverse(pos + 1, elementCount) ProcedureReturn #True ;next lexicographic permutation found EndProcedure Procedure display(Array a(1)) Protected i, fin = ArraySize(a()) For i = 0 To fin Print(Str(a(i))) If i = fin: Continue: EndIf Print(", ") Next PrintN("") EndProcedure If OpenConsole() Dim a(2) a(0) = 1: a(1) = 2: a(2) = 3 display(a()) While nextPermutation(a()): display(a()): Wend Print(#CRLF$ + #CRLF$+ "Press ENTER to exit"): Input() CloseConsole() EndIf Output: 1, 2, 3 1, 3, 2 2, 1, 3 2, 3, 1 3, 1, 2 3, 2, 1 ## Python ### Standard library function Works with: Python version 2.6+ import itertools for values in itertools.permutations([1,2,3]): print (values) Output: (1, 2, 3) (1, 3, 2) (2, 1, 3) (2, 3, 1) (3, 1, 2) (3, 2, 1) ### Recursive implementation The follwing functions start from a list [0 ... n-1] and exchange elements to always have a valid permutation. This is done recursively: first exchange a[0] with all the other elements, then a[1] with a[2] ... a[n-1], etc. thus yielding all permutations. def perm1(n): a = list(range(n)) def sub(i): if i == n - 1: yield tuple(a) else: for k in range(i, n): a[i], a[k] = a[k], a[i] yield from sub(i + 1) a[i], a[k] = a[k], a[i] yield from sub(0) def perm2(n): a = list(range(n)) def sub(i): if i == n - 1: yield tuple(a) else: for k in range(i, n): a[i], a[k] = a[k], a[i] yield from sub(i + 1) x = a[i] for k in range(i + 1, n): a[k - 1] = a[k] a[n - 1] = x yield from sub(0) These two solutions make use of a generator, and "yield from" introduced in PEP-380. They are slightly different: the latter produces permutations in lexicographic order, because the "remaining" part of a (that is, a[i+1:]) is always sorted, whereas the former always reverses the exchange just after the recursive call. On three elements, the difference can be seen on the last two permutations: for u in perm1(3): print(u) (0, 1, 2) (0, 2, 1) (1, 0, 2) (1, 2, 0) (2, 1, 0) (2, 0, 1) for u in perm2(3): print(u) (0, 1, 2) (0, 2, 1) (1, 0, 2) (1, 2, 0) (2, 0, 1) (2, 1, 0) ### Iterative implementation Given a permutation, one can easily compute the next permutation in some order, for example lexicographic order, here. Then to get all permutations, it's enough to start from [0, 1, ... n-1], and store the next permutation until [n-1, n-2, ... 0], which is the last in lexicographic order. def nextperm(a): n = len(a) i = n - 1 while i > 0 and a[i - 1] > a[i]: i -= 1 j = i k = n - 1 while j < k: a[j], a[k] = a[k], a[j] j += 1 k -= 1 if i == 0: return False else: j = i while a[j] < a[i - 1]: j += 1 a[i - 1], a[j] = a[j], a[i - 1] return True def perm3(n): if type(n) is int: if n < 1: return [] a = list(range(n)) else: a = sorted(n) u = [tuple(a)] while nextperm(a): u.append(tuple(a)) return u for p in perm3(3): print(p) (0, 1, 2) (0, 2, 1) (1, 0, 2) (1, 2, 0) (2, 0, 1) (2, 1, 0) ### Implementation using destructive list updates def permutations(xs): ac = [[]] for x in xs: ac_new = [] for ts in ac: for n in range(0,ts.__len__()+1): new_ts = ts[:] #(shallow) copy of ts new_ts.insert(n,x) ac_new.append(new_ts) ac=ac_new return ac print(permutations([1,2,3,4])) ### Functional :: type-preserving The itertools.permutations function is polymorphic in its inputs but not in its outputs – it discards the type of input lists and strings, coercing all inputs to tuples. In this type-preserving variant, permutation is defined (without the need for mutating name-bindings) in terms of two universal abstractions: reduce and concatMap: Works with: Python version 3.7 '''Permutations of a list, string or tuple''' from functools import (reduce) from itertools import (chain) # permutations :: [a] -> [[a]] def permutations(xs): '''Type-preserving permutations of xs. ''' ps = reduce( lambda a, x: concatMap( lambda xs: ( xs[n:] + [x] + xs[0:n] for n in range(0, 1 + len(xs))) )(a), xs, [[]] ) t = type(xs) return ps if list == t else ( [''.join(x) for x in ps] if str == t else [ t(x) for x in ps ] ) # TEST ---------------------------------------------------- # main :: IO () def main(): '''Permutations of lists, strings and tuples.''' print( fTable(__doc__ + ':\n')(repr)(showList)( permutations )([ [1, 2, 3], 'abc', (1, 2, 3), ]) ) # GENERIC ------------------------------------------------- # concatMap :: (a -> [b]) -> [a] -> [b] def concatMap(f): '''A concatenated list over which a function has been mapped. The list monad can be derived by using a function f which wraps its output in a list, (using an empty list to represent computational failure).''' return lambda xs: list( chain.from_iterable(map(f, xs)) ) # FORMATTING ---------------------------------------------- # fTable :: String -> (a -> String) -> # (b -> String) -> (a -> b) -> [a] -> String def fTable(s): '''Heading -> x display function -> fx display function -> f -> xs -> tabular string. ''' def go(xShow, fxShow, f, xs): ys = [xShow(x) for x in xs] w = max(map(len, ys)) return s + '\n' + '\n'.join(map( lambda x, y: y.rjust(w, ' ') + ' -> ' + fxShow(f(x)), xs, ys )) return lambda xShow: lambda fxShow: lambda f: lambda xs: go( xShow, fxShow, f, xs ) # showList :: [a] -> String def showList(xs): '''Stringification of a list.''' return '[' + ','.join(showList(x) for x in xs) + ']' if ( isinstance(xs, list) ) else repr(xs) # MAIN --- if __name__ == '__main__': main() Output: [1, 2, 3] -> [[1,2,3],[2,3,1],[3,1,2],[2,1,3],[1,3,2],[3,2,1]] 'abc' -> ['abc','bca','cab','bac','acb','cba'] (1, 2, 3) -> [(1, 2, 3),(2, 3, 1),(3, 1, 2),(2, 1, 3),(1, 3, 2),(3, 2, 1)] ## QBasic Works with: QBasic version 1.1 Works with: QuickBasic version 4.5 Translation of: FreeBASIC SUB perms (n) DIM a(0 TO n - 1), c(0 TO n - 1) FOR j = 0 TO n - 1 a(j) = j + 1 PRINT a(j); NEXT j PRINT i = 0 WHILE i < n IF c(i) < i THEN IF (i AND 1) = 0 THEN SWAP a(0), a(i) ELSE SWAP a(c(i)), a(i) END IF FOR j = 0 TO n - 1 PRINT a(j); NEXT j PRINT c(i) = c(i) + 1 i = 0 ELSE c(i) = 0 i = i + 1 END IF WEND END SUB perms(4) ## Qi Translation of: Erlang (define insert L 0 E -> [E|L] [L|Ls] N E -> [L|(insert Ls (- N 1) E)]) (define seq Start Start -> [Start] Start End -> [Start|(seq (+ Start 1) End)]) (define append-lists [] -> [] [A|B] -> (append A (append-lists B))) (define permutate [] -> [[]] [H|T] -> (append-lists (map (/. P (map (/. N (insert P N H)) (seq 0 (length P)))) (permute T)))) ## Quackery ### General Solution The word perms solves a more general task; generate permutations of between a and b items (inclusive) from the specified nest. [ stack ] is perms.min ( --> [ ) [ stack ] is perms.max ( --> [ ) forward is (perms) [ over size perms.min share > if [ over temp take swap nested join temp put ] over size perms.max share < if [ dup size times [ 2dup i^ pluck rot swap nested join swap (perms) ] ] 2drop ] resolves (perms) ( [ [ --> ) [ perms.max put 1 - perms.min put [] temp put [] swap (perms) temp take perms.min release perms.max release ] is perms ( [ a b --> [ ) [ dup size dup perms ] is permutations ( [ --> [ ) ' [ 1 2 3 ] permutations echo cr$ "quack" permutations 60 wrap "quack" 3 4 perms 46 wrap$Output: [ [ 1 2 3 ] [ 1 3 2 ] [ 2 1 3 ] [ 2 3 1 ] [ 3 1 2 ] [ 3 2 1 ] ] quack quakc qucak qucka qukac qukca qauck qaukc qacuk qacku qakuc qakcu qcuak qcuka qcauk qcaku qckua qckau qkuac qkuca qkauc qkacu qkcua qkcau uqack uqakc uqcak uqcka uqkac uqkca uaqck uaqkc uacqk uackq uakqc uakcq ucqak ucqka ucaqk ucakq uckqa uckaq ukqac ukqca ukaqc ukacq ukcqa ukcaq aquck aqukc aqcuk aqcku aqkuc aqkcu auqck auqkc aucqk auckq aukqc aukcq acquk acqku acuqk acukq ackqu ackuq akquc akqcu akuqc akucq akcqu akcuq cquak cquka cqauk cqaku cqkua cqkau cuqak cuqka cuaqk cuakq cukqa cukaq caquk caqku cauqk caukq cakqu cakuq ckqua ckqau ckuqa ckuaq ckaqu ckauq kquac kquca kqauc kqacu kqcua kqcau kuqac kuqca kuaqc kuacq kucqa kucaq kaquc kaqcu kauqc kaucq kacqu kacuq kcqua kcqau kcuqa kcuaq kcaqu kcauq qua quac quak quc quca quck quk quka qukc qau qauc qauk qac qacu qack qak qaku qakc qcu qcua qcuk qca qcau qcak qck qcku qcka qku qkua qkuc qka qkau qkac qkc qkcu qkca uqa uqac uqak uqc uqca uqck uqk uqka uqkc uaq uaqc uaqk uac uacq uack uak uakq uakc ucq ucqa ucqk uca ucaq ucak uck uckq ucka ukq ukqa ukqc uka ukaq ukac ukc ukcq ukca aqu aquc aquk aqc aqcu aqck aqk aqku aqkc auq auqc auqk auc aucq auck auk aukq aukc acq acqu acqk acu acuq acuk ack ackq acku akq akqu akqc aku akuq akuc akc akcq akcu cqu cqua cquk cqa cqau cqak cqk cqku cqka cuq cuqa cuqk cua cuaq cuak cuk cukq cuka caq caqu caqk cau cauq cauk cak cakq caku ckq ckqu ckqa cku ckuq ckua cka ckaq ckau kqu kqua kquc kqa kqau kqac kqc kqcu kqca kuq kuqa kuqc kua kuaq kuac kuc kucq kuca kaq kaqu kaqc kau kauq kauc kac kacq kacu kcq kcqu kcqa kcu kcuq kcua kca kcaq kcau ### An Uncommon Ordering Edit: I think this process is called "iterative deepening". Would love to have this confirmed or corrected. The central idea is that given a list of the permutations of say 3 items, each permutation can be used to generate 4 of the permutations of 4 items, so for example, from [ 3 1 2 ] we can generate [ 0 3 1 2 ] [ 3 0 1 2 ] [ 3 1 0 2 ] [ 3 1 2 0 ] by stuffing the 0 into each of the 4 possible positions that it could go. The code start with a nest of all the permutations of 0 items [ [ ] ], and each time though the outer times loop (i.e. 4 times in the example) it takes each of the permutations generated so far (this is the witheach loop) and applies the central idea descried above (that is the inner times loop.) Some aids to reading the code. Quackery is a stack based language. If you are unfamiliar the with words swap, rot, dup, 2dup, dip, unrot or drop they can be skimmed over as "noise" to get a gist of the process. [] creates an empty nest [ ]. times indicates that the word or nest following it is to be repeated a specified number of times. (The specified number is on the top of the stack, so 4 times [ ... ]repeats some arbitrary code 4 times.) i returns the number of times a times loop has left to repeat. It counts down to zero. i^ returns the number of times a times loop has been repeated. It counts up from zero. size returns the number of items (words, numbers, nests) in a nest. witheach indicates that the word or nest following it is to be repeated once for each item in a specified nest, with successive items from the nest available on the top of stack on each repetition. 999 ' [ 10 11 12 13 ] 3 stuff will return [ 10 11 12 999 13 ]by stuffing the number 999 into the 3rd position in the nest. (The start of a nest is the zeroth position, the end of this nest is the 5th position.) nested join adds a nest to the end of a nest as its last item. [ ' [ [ ] ] swap times [ [] i rot witheach [ dup size 1+ times [ 2dup i^ stuff dip rot nested join unrot ] drop ] drop ] ] is perms ( n --> [ ) 4 perms witheach [ echo cr ] Output: [ 0 1 2 3 ] [ 1 0 2 3 ] [ 1 2 0 3 ] [ 1 2 3 0 ] [ 0 2 1 3 ] [ 2 0 1 3 ] [ 2 1 0 3 ] [ 2 1 3 0 ] [ 0 2 3 1 ] [ 2 0 3 1 ] [ 2 3 0 1 ] [ 2 3 1 0 ] [ 0 1 3 2 ] [ 1 0 3 2 ] [ 1 3 0 2 ] [ 1 3 2 0 ] [ 0 3 1 2 ] [ 3 0 1 2 ] [ 3 1 0 2 ] [ 3 1 2 0 ] [ 0 3 2 1 ] [ 3 0 2 1 ] [ 3 2 0 1 ] [ 3 2 1 0 ] ## R ### Iterative version next.perm <- function(a) { n <- length(a) i <- n while (i > 1 && a[i - 1] >= a[i]) i <- i - 1 if (i == 1) { NULL } else { j <- i k <- n while (j < k) { s <- a[j] a[j] <- a[k] a[k] <- s j <- j + 1 k <- k - 1 } s <- a[i - 1] j <- i while (a[j] <= s) j <- j + 1 a[i - 1] <- a[j] a[j] <- s a } } perm <- function(n) { e <- NULL a <- 1:n repeat { e <- cbind(e, a) a <- next.perm(a) if (is.null(a)) break } unname(e) } Example > perm(3) [,1] [,2] [,3] [,4] [,5] [,6] [1,] 1 1 2 2 3 3 [2,] 2 3 1 3 1 2 [3,] 3 2 3 1 2 1 ### Recursive version # list of the vectors by inserting x in s at position 0...end. linsert <- function(x,s) lapply(0:length(s), function(k) append(s,x,k)) # list of all permutations of 1:n perm <- function(n){ if (n == 1) list(1) else unlist(lapply(perm(n-1), function(s) linsert(n,s)), recursive = F)} # permutations of a vector s permutation <- function(s) lapply(perm(length(s)), function(i) s[i]) Output: > permutation(letters[1:3]) [[1]] [1] "c" "b" "a" [[2]] [1] "b" "c" "a" [[3]] [1] "b" "a" "c" [[4]] [1] "c" "a" "b" [[5]] [1] "a" "c" "b" [[6]] [1] "a" "b" "c" ## Racket #lang racket ;; using a builtin (permutations '(A B C)) ;; -> '((A B C) (B A C) (A C B) (C A B) (B C A) (C B A)) ;; a random simple version (which is actually pretty good for a simple version) (define (perms l) (let loop ([l l] [tail '()]) (if (null? l) (list tail) (append-map (λ(x) (loop (remq x l) (cons x tail))) l)))) (perms '(A B C)) ;; -> '((C B A) (B C A) (C A B) (A C B) (B A C) (A B C)) ;; permutations in lexicographic order (define (lperms s) (cond [(empty? s) '()] [(empty? (cdr s)) (list s)] [else (let splice ([l '()][m (car s)][r (cdr s)]) (append (map (lambda (x) (cons m x)) (lperms (append l r))) (if (empty? r) '() (splice (append l (list m)) (car r) (cdr r)))))])) (display (lperms '(A B C))) ;; -> ((A B C) (A C B) (B A C) (B C A) (C A B) (C B A)) ;; permutations in lexicographical order using generators (require racket/generator) (define (splice s) (generator () (let outer-loop ([l '()][m (car s)][r (cdr s)]) (let ([permuter (lperm (append l r))]) (let inner-loop ([p (permuter)]) (when (not (void? p)) (let ([q (cons m p)]) (yield q) (inner-loop (permuter)))))) (if (not (empty? r)) (outer-loop (append l (list m)) (car r) (cdr r)) (void))))) (define (lperm s) (generator () (cond [(empty? s) (yield '())] [(empty? (cdr s)) (yield s)] [else (let ([splicer (splice s)]) (let loop ([q (splicer)]) (when (not (void? q)) (begin (yield q) (loop (splicer))))))]) (void))) (let ([permuter (lperm '(A B C))]) (let next-perm ([p (permuter)]) (when (not (void? p)) (begin (display p) (next-perm (permuter)))))) ;; -> (A B C)(A C B)(B A C)(B C A)(C A B)(C B A) ## Raku (formerly Perl 6) Works with: rakudo version 2018.10 First, you can just use the built-in method on any list type. .say for <a b c>.permutations Output: a b c a c b b a c b c a c a b c b a Here is some generic code that works with any ordered type. To force lexicographic ordering, change after to gt. To force numeric order, replace it with >. sub next_perm ( @a is copy ) { my$j = @a.end - 1;
return Nil if --$j < 0 while @a[$j] after @a[$j+1]; my$aj = @a[$j]; my$k = @a.end;
$k-- while$aj after @a[$k]; @a[$j, $k ] .= reverse; my$r = @a.end;
my $s =$j + 1;
@a[ $r--,$s++ ] .= reverse while $r >$s;
return @a;
}

.say for [<a b c>], &next_perm ...^ !*;
Output:
a b c
a c b
b a c
b c a
c a b
c b a

Here is another non-recursive implementation, which returns a lazy list. It also works with any type.

sub permute(+@items) {
my @seq := 1..+@items;
gather for (^[*] @seq) -> $n is copy { my @order; for @seq { unshift @order,$n mod $_;$n div= $_; } my @i-copy = @items; take map { |@i-copy.splice($_, 1) }, @order;
}
}
.say for permute( 'a'..'c' )
Output:
(a b c)
(a c b)
(b a c)
(b c a)
(c a b)
(c b a)

Finally, if you just want zero-based numbers, you can call the built-in function:

.say for permutations(3);
Output:
0 1 2
0 2 1
1 0 2
1 2 0
2 0 1
2 1 0

## RATFOR

For translation to FORTRAN 77 with the public domain ratfor77 preprocessor.

# Heap’s algorithm for generating permutations. Algorithm 2 in
# Robert Sedgewick, 1977. Permutation generation methods. ACM
# Comput. Surv. 9, 2 (June 1977), 137-164.

define(n, 3)
define(n_minus_1, 2)

implicit none

integer a(1:n)

integer c(1:n)
integer i, k
integer tmp

10000 format ('(', I1, n_minus_1(' ', I1), ')')

# Initialize the data to be permuted.
do i = 1, n {
a(i) = i
}

# What follows is a non-recursive Heap’s algorithm as presented by
# Sedgewick. Sedgewick neglects to fully initialize c, so I have
# corrected for that. Also I compute k without branching, by instead
# doing a little arithmetic.
do i = 1, n {
c(i) = 1
}
i = 2
write (*, 10000) a
while (i <= n) {
if (c(i) < i) {
k = mod (i, 2) + ((1 - mod (i, 2)) * c(i))
tmp = a(i)
a(i) = a(k)
a(k) = tmp
c(i) = c(i) + 1
i = 2
write (*, 10000) a
} else {
c(i) = 1
i = i + 1
}
}

end

Here is what the generated FORTRAN 77 code looks like:

C Output from Public domain Ratfor, version 1.0
implicit none
integer a(1: 3)
integer c(1: 3)
integer i, k
integer tmp
10000 format ('(', i1, 2(' ', i1), ')')
do23000 i = 1, 3
a(i) = i
23000 continue
23001 continue
do23002 i = 1, 3
c(i) = 1
23002 continue
23003 continue
i = 2
write (*, 10000) a
23004 if(i .le. 3)then
if(c(i) .lt. i)then
k = mod (i, 2) + ((1 - mod (i, 2)) * c(i))
tmp = a(i)
a(i) = a(k)
a(k) = tmp
c(i) = c(i) + 1
i = 2
write (*, 10000) a
else
c(i) = 1
i = i + 1
endif
goto 23004
endif
23005 continue
end
Output:

$ratfor77 permutations.r > permutations.f && f2c permutations.f && cc -o permutations permutations.c -lf2c && ./permutations (1 2 3) (2 1 3) (3 1 2) (1 3 2) (2 3 1) (3 2 1) ## REXX This program could be simplified quite a bit if the "things" were just restricted to numbers (numerals), but that would make it specific to numbers and not "things" or objects. /*REXX pgm generates/displays all permutations of N different objects taken M at a time.*/ parse arg things bunch inbetweenChars names /*obtain optional arguments from the CL*/ if things=='' | things=="," then things= 3 /*Not specified? Then use the default.*/ if bunch=='' | bunch=="," then bunch= things /* " " " " " " */ /* ╔════════════════════════════════════════════════════════════════╗ */ /* ║ inBetweenChars (optional) defaults to a [null]. ║ */ /* ║ names (optional) defaults to digits (and letters).║ */ /* ╚════════════════════════════════════════════════════════════════╝ */ call permSets things, bunch, inBetweenChars, names exit /*stick a fork in it, we're all done. */ /*──────────────────────────────────────────────────────────────────────────────────────*/ p: return word( arg(1), 1) /*P function (Pick first arg of many).*/ /*──────────────────────────────────────────────────────────────────────────────────────*/ permSets: procedure; parse arg x,y,between,uSyms /*X things taken Y at a time. */ @.=; sep= /*X can't be > length(@0abcs). */ @abc = 'abcdefghijklmnopqrstuvwxyz'; @abcU= @abc; upper @abcU @abcS = @abcU || @abc; @0abcS= 123456789 || @abcS do k=1 for x /*build a list of permutation symbols. */ _= p(word(uSyms, k) p(substr(@0abcS, k, 1) k) ) /*get/generate a symbol.*/ if length(_)\==1 then sep= '_' /*if not 1st character, then use sep. */$.k= _ /*append the character to symbol list. */
end /*k*/

if between=='' then between= sep /*use the appropriate separator chars. */
return /* [↓] this is a recursive subroutine.*/
.permSet: procedure expose $. @. between x y; parse arg ? if ?>y then do; _= @.1; do j=2 for y-1 _= _ || between || @.j end /*j*/ say _ end else do q=1 for x /*build the permutation recursively. */ do k=1 for ?-1; if @.k==$.q then iterate q
end /*k*/
@.?= $.q; call .permSet ?+1 end /*q*/ return output when the following was used for input: 3 3 123 132 213 231 312 321 output when the following was used for input: 4 4 --- A B C D A---B---C---D A---B---D---C A---C---B---D A---C---D---B A---D---B---C A---D---C---B B---A---C---D B---A---D---C B---C---A---D B---C---D---A B---D---A---C B---D---C---A C---A---B---D C---A---D---B C---B---A---D C---B---D---A C---D---A---B C---D---B---A D---A---B---C D---A---C---B D---B---A---C D---B---C---A D---C---A---B D---C---B---A output when the following was used for input: 4 3 ~ aardvark gnu stegosaurus platypus aardvark~gnu~stegosaurus aardvark~gnu~platypus aardvark~stegosaurus~gnu aardvark~stegosaurus~platypus aardvark~platypus~gnu aardvark~platypus~stegosaurus gnu~aardvark~stegosaurus gnu~aardvark~platypus gnu~stegosaurus~aardvark gnu~stegosaurus~platypus gnu~platypus~aardvark gnu~platypus~stegosaurus stegosaurus~aardvark~gnu stegosaurus~aardvark~platypus stegosaurus~gnu~aardvark stegosaurus~gnu~platypus stegosaurus~platypus~aardvark stegosaurus~platypus~gnu platypus~aardvark~gnu platypus~aardvark~stegosaurus platypus~gnu~aardvark platypus~gnu~stegosaurus platypus~stegosaurus~aardvark platypus~stegosaurus~gnu ## Ring load "stdlib.ring" list = 1:4 lenList = len(list) permut = [] for perm = 1 to factorial(len(list)) for i = 1 to len(list) add(permut,list[i]) next perm(list) next for n = 1 to len(permut)/lenList for m = (n-1)*lenList+1 to n*lenList see "" + permut[m] if m < n*lenList see "," ok next see nl next func perm a elementcount = len(a) if elementcount < 1 then return ok pos = elementcount-1 while a[pos] >= a[pos+1] pos -= 1 if pos <= 0 permutationReverse(a, 1, elementcount) return ok end last = elementcount while a[last] <= a[pos] last -= 1 end temp = a[pos] a[pos] = a[last] a[last] = temp permReverse(a, pos+1, elementcount) func permReverse a, first, last while first < last temp = a[first] a[first] = a[last] a[last] = temp first += 1 last -= 1 end Output: 1,2,3,4 1,2,4,3 1,3,2,4 1,3,4,2 1,4,2,3 1,4,3,2 2,1,3,4 2,1,4,3 2,3,1,4 2,3,4,1 2,4,1,3 2,4,3,1 3,1,2,4 3,1,4,2 3,2,1,4 3,2,4,1 3,4,1,2 3,4,2,1 4,1,2,3 4,1,3,2 4,2,1,3 4,2,3,1 4,3,1,2 4,3,2,1 ## Ring Another Solution // Permutations -- Bert Mariani 2020-07-12 // Ask User for number of digits to permutate ? "Enter permutations number : " Give n n = number(n) x = 1:n // array ? "Permutations are : " count = 0 nPermutation(1,n) //===>>> START ? " " // ? = print ? "Exiting of the program... " ? "Enter to Exit : " Give m // To Exit CMD window //====================== // Returns true only if uniq number on row Func Place(k,i) for j=1 to k-1 if x[j] = i // Two numbers in same row return 0 ok next return 1 //====================== Func nPermutation(k, n) for i = 1 to n if( Place(k,i)) //===>>> Call x[k] = i if(k=n) See nl for i= 1 to n See " "+ x[i] next See " "+ (count++) else nPermutation(k+1,n) //===>>> Call RECURSION ok ok next return Output: Enter permutations number : 4 Permutations are : 1 2 3 4 1 2 4 3 1 3 2 4 1 3 4 2 1 4 2 3 1 4 3 2 2 1 3 4 2 1 4 3 2 3 1 4 2 3 4 1 2 4 1 3 2 4 3 1 3 1 2 4 3 1 4 2 3 2 1 4 3 2 4 1 3 4 1 2 3 4 2 1 4 1 2 3 4 1 3 2 4 2 1 3 4 2 3 1 4 3 1 2 4 3 2 1 Exiting of the program... Enter to Exit : ## Ruby p [1,2,3].permutation.to_a Output: [[1, 2, 3], [1, 3, 2], [2, 1, 3], [2, 3, 1], [3, 1, 2], [3, 2, 1]] ## Run BASIC Works with Run BASIC, Liberty BASIC and Just BASIC list$ = "h,e,l,l,o"		' supply list seperated with comma's

while word$(list$,d+1,",") <> "" 'Count how many in the list
d = d + 1
wend

dim theList$(d) ' place list in array for i = 1 to d theList$(i) = word$(list$,i,",")
next i

for i = 1 to d ' print the Permutations
for j = 2 to d
perm$= "" for k = 1 to d perm$ = perm$+ theList$(k)
next k
if instr(perm2$,perm$+",") = 0 then print perm$' only list 1 time perm2$ = perm2$+ perm$ + ","
h$= theList$(j)
theList$(j) = theList$(j - 1)
theList$(j - 1) = h$
next j
next i
end
Output:
hello
ehllo
elhlo
ellho
elloh
leloh
lleoh
lloeh
llohe
lolhe
lohle
lohel
olhel
ohlel
ohell
hoell
heoll
helol

## Rust

### Iterative

Uses Heap's algorithm. An in-place version is possible but is incompatible with Iterator.

pub fn permutations(size: usize) -> Permutations {
Permutations { idxs: (0..size).collect(), swaps: vec![0; size], i: 0 }
}

pub struct Permutations {
idxs: Vec<usize>,
swaps: Vec<usize>,
i: usize,
}

impl Iterator for Permutations {
type Item = Vec<usize>;

fn next(&mut self) -> Option<Self::Item> {
if self.i > 0 {
loop {
if self.i >= self.swaps.len() { return None; }
if self.swaps[self.i] < self.i { break; }
self.swaps[self.i] = 0;
self.i += 1;
}
self.idxs.swap(self.i, (self.i & 1) * self.swaps[self.i]);
self.swaps[self.i] += 1;
}
self.i = 1;
Some(self.idxs.clone())
}
}

fn main() {
let perms = permutations(3).collect::<Vec<_>>();
assert_eq!(perms, vec![
vec![0, 1, 2],
vec![1, 0, 2],
vec![2, 0, 1],
vec![0, 2, 1],
vec![1, 2, 0],
vec![2, 1, 0],
]);
}

### Recursive

use std::collections::VecDeque;

fn permute<T, F: Fn(&[T])>(used: &mut Vec<T>, unused: &mut VecDeque<T>, action: &F) {
if unused.is_empty() {
action(used);
} else {
for _ in 0..unused.len() {
used.push(unused.pop_front().unwrap());
permute(used, unused, action);
unused.push_back(used.pop().unwrap());
}
}
}

fn main() {
let mut queue = (1..4).collect::<VecDeque<_>>();
permute(&mut Vec::new(), &mut queue, &|perm| println!("{:?}", perm));
}

## SAS

/* Store permutations in a SAS dataset. Translation of Fortran 77 */
data perm;
n=6;
array a{6} p1-p6;
do i=1 to n;
a(i)=i;
end;
L1:
output;
if next then goto L1;
stop;
L2:
next=0;
i=n-1;
L10:
if a(i)<a(i+1) then goto L20;
i=i-1;
if i=0 then goto L20;
goto L10;
L20:
j=i+1;
k=n;
L30:
t=a(j);
a(j)=a(k);
a(k)=t;
j=j+1;
k=k-1;
if j<k then goto L30;
j=i;
if j=0 then return;
L40:
j=j+1;
if a(j)<a(i) then goto L40;
t=a(i);
a(i)=a(j);
a(j)=t;
next=1;
return;
keep p1-p6;
run;

## Scala

There is a built-in function in the Scala collections library, that is part of the language's standard library. The permutation function is available on any sequential collection. It could be used as follows given a list of numbers:

List(1, 2, 3).permutations.foreach(println)
Output:
List(1, 2, 3)
List(1, 3, 2)
List(2, 1, 3)
List(2, 3, 1)
List(3, 1, 2)
List(3, 2, 1)

The following function returns all the permutations of a list:

def permutations[T]: List[T] => Traversable[List[T]] = {
case Nil => List(Nil)
case xs => {
for {
(x, i) <- xs.zipWithIndex
ys <- permutations(xs.take(i) ++ xs.drop(1 + i))
} yield {
x :: ys
}
}
}

If you need the unique permutations, use distinct or toSet on either the result or on the input.

## Scheme

Translation of: Erlang
(define (insert l n e)
(if (= 0 n)
(cons e l)
(cons (car l)
(insert (cdr l) (- n 1) e))))

(define (seq start end)
(if (= start end)
(list end)
(cons start (seq (+ start 1) end))))

(define (permute l)
(if (null? l)
'(())
(apply append (map (lambda (p)
(map (lambda (n)
(insert p n (car l)))
(seq 0 (length p))))
(permute (cdr l))))))
Translation of: OCaml
; translation of ocaml : mostly iterative, with auxiliary recursive functions for some loops
(define (vector-swap! v i j)
(let ((tmp (vector-ref v i)))
(vector-set! v i (vector-ref v j))
(vector-set! v j tmp)))

(define (next-perm p)
(let* ((n (vector-length p))
(i (let aux ((i (- n 2)))
(if (or (< i 0) (< (vector-ref p i) (vector-ref p (+ i 1))))
i (aux (- i 1))))))
(let aux ((j (+ i 1)) (k (- n 1)))
(if (< j k) (begin (vector-swap! p j k) (aux (+ j 1) (- k 1)))))
(if (< i 0) #f (begin
(vector-swap! p i (let aux ((j (+ i 1)))
(if (> (vector-ref p j) (vector-ref p i)) j (aux (+ j 1)))))
#t))))

(define (print-perm p)
(let ((n (vector-length p)))
(do ((i 0 (+ i 1))) ((= i n)) (display (vector-ref p i)) (display " "))
(newline)))

(define (print-all-perm n)
(let ((p (make-vector n)))
(do ((i 0 (+ i 1))) ((= i n)) (vector-set! p i i))
(print-perm p)
(do ( ) ((not (next-perm p))) (print-perm p))))

(print-all-perm 3)
; 0 1 2
; 0 2 1
; 1 0 2
; 1 2 0
; 2 0 1
; 2 1 0

;a more recursive implementation
(define (permute p i)
(let ((n (vector-length p)))
(if (= i (- n 1)) (print-perm p)
(begin
(do ((j i (+ j 1))) ((= j n))
(vector-swap! p i j)
(permute p (+ i 1)))
(do ((j (- n 1) (- j 1))) ((< j i))
(vector-swap! p i j))))))

(define (print-all-perm-rec n)
(let ((p (make-vector n)))
(do ((i 0 (+ i 1))) ((= i n)) (vector-set! p i i))
(permute p 0)))

(print-all-perm-rec 3)
; 0 1 2
; 0 2 1
; 1 0 2
; 1 2 0
; 2 0 1
; 2 1 0

Completely recursive on lists:

(define (perm s)
(cond ((null? s) '())
((null? (cdr s)) (list s))
(else ;; extract each item in list in turn and perm the rest
(let splice ((l '()) (m (car s)) (r (cdr s)))
(append
(map (lambda (x) (cons m x)) (perm (append l r)))
(if (null? r) '()
(splice (cons m l) (car r) (cdr r))))))))

(display (perm '(1 2 3)))

## Seed7

$include "seed7_05.s7i"; const type: permutations is array array integer; const func permutations: permutations (in array integer: items) is func result var permutations: permsList is 0 times 0 times 0; local const proc: perms (in array integer: sequence, in array integer: prefix) is func local var integer: element is 0; var integer: index is 0; begin if length(sequence) <> 0 then for element key index range sequence do perms(sequence[.. pred(index)] & sequence[succ(index) ..], prefix & [] (element)); end for; else permsList &:= prefix; end if; end func; begin perms(items, 0 times 0); end func; const proc: main is func local var array integer: perm is 0 times 0; var integer: element is 0; begin for perm range permutations([] (1, 2, 3)) do for element range perm do write(element <& " "); end for; writeln; end for; end func; Output: 1 2 3 1 3 2 2 1 3 2 3 1 3 1 2 3 2 1 ## Shen (define permute [] -> [] [X] -> [[X]] X -> (permute-helper [] X)) (define permute-helper _ [] -> [] Done [X|Rest] -> (append (prepend-all X (permute (append Done Rest))) (permute-helper [X|Done] Rest)) ) (define prepend-all _ [] -> [] X [Next|Rest] -> [[X|Next]|(prepend-all X Rest)] ) (set *maximum-print-sequence-size* 50) (permute [a b c d]) Output: [[a b c d] [a b d c] [a c b d] [a c d b] [a d c b] [a d b c] [b a c d] [b a d c] [b c a d] [b c d a] [b d c a] [b d a c] [c b a d] [c b d a] [c a b d] [c a d b] [c d a b] [c d b a] [d c b a] [d c a b] [d b c a] [d b a c] [d a b c] [d a c b]] For lexical order, make a small change: (define permute-helper _ [] -> [] Done [X|Rest] -> (append (prepend-all X (permute (append Done Rest))) (permute-helper (append Done [X]) Rest)) ) ## Sidef ### Built-in [0,1,2].permutations { |p| say p } ### Iterative func forperm(callback, n) { var idx = @^n loop { callback([idx...]) var p = n-1 while (idx[p-1] > idx[p]) {--p} p == 0 && return() var d = p idx += idx.splice(p).reverse while (idx[p-1] > idx[d]) {++d} idx.swap(p-1, d) } return() } forperm({|p| say p }, 3) ### Recursive func permutations(callback, set, perm=[]) { set.is_empty && callback(perm) for i in ^set { __FUNC__(callback, [ set[(0 ..^ i)..., (i+1 ..^ set.len)...] ], [perm..., set[i]]) } return() } permutations({|p| say p }, [0,1,2]) Output: [0, 1, 2] [0, 2, 1] [1, 0, 2] [1, 2, 0] [2, 0, 1] [2, 1, 0] ## Smalltalk Works with: Squeak Works with: Pharo (1 to: 4) permutationsDo: [ :x | Transcript show: x printString; cr ]. Works with: GNU Smalltalk ArrayedCollection extend [ permuteAndDo: aBlock ["Permute receiver in-place, and call aBlock. Requires integer keys." self permuteUpto: self size andDo: aBlock] permuteUpto: n andDo: aBlock [n = 0 ifTrue: [^aBlock value]. 1 to: n do: [:i | self swap: i with: n. self permuteUpto: n-1 andDo: aBlock. self swap: i with: n]] ] SequenceableCollection extend [ permutations ["Answer a ReadStream of permuted shallow copies of receiver." | c | c := MappedCollection collection: self map: self keys asArray. ^Generator on: [:g | c map permuteAndDo: [g yield: (c copyFrom: 1 to: c size)]]] Use example: st> 'Abc' permutations contents ('bcA' 'cbA' 'cAb' 'Acb' 'bAc' 'Abc' ) ## Stata Program to build a dataset containing all permutations of 1...n. Each permutation is stored as an observation. For instance: perm 4 Program program perm local n=1' local r=1 forv i=1/n' { local r=r'*i' } clear qui set obs r' forv i=1/n' { gen p`i'=0 } mata: genperm() end mata void genperm() { real scalar n, i, j, k, s, p real rowvector u st_view(a=., ., .) n = cols(a) u = 1..n p = 1 do { a[p++, .] = u for (i = n; i > 1; i--) { if (u[i-1] < u[i]) break } if (i > 1) { j = i k = n while (j < k) u[(j++, k--)] = u[(k, j)] s = u[i-1] for (j = i; u[j] < s; j++) { } u[i-1] = u[j] u[j] = s } } while (i > 1) } end ## Swift func perms<T>(var ar: [T]) -> [[T]] { return heaps(&ar, ar.count) } func heaps<T>(inout ar: [T], n: Int) -> [[T]] { return n == 1 ? [ar] : Swift.reduce(0..<n, [[T]]()) { (var shuffles, i) in shuffles.extend(heaps(&ar, n - 1)) swap(&ar[n % 2 == 0 ? i : 0], &ar[n - 1]) return shuffles } } perms([1, 2, 3]) // [[1, 2, 3], [2, 1, 3], [3, 1, 2], [1, 3, 2], [2, 3, 1], [3, 2, 1]] ## Tailspin This solution seems to be the same as the Kotlin solution. Permutations flow independently without being collected until the end. templates permutations when <=1> do [1] ! otherwise def n:$;
templates expand
def p: $; 1..$n -> $$def k: ; [p(1..k-1)..., n, p(k..last)...] !$$ !
end expand
$n - 1 -> permutations -> expand ! end permutations def alpha: ['ABCD'...]; [$alpha::length -> permutations -> '$alpha($)...;' ] -> !OUT::write

Output:

If we collect all the permutations of the next size down, we can output permutations in lexical order

templates lexicalPermutations
when <=1> do [1] !
otherwise
def n: $; def p: [$n - 1 -> lexicalPermutations ];
1..$n -> $$def k: ; p... -> [ k, ... -> \(when <k..> do +1! otherwise !$$] !\) ! end lexicalPermutations def alpha: ['ABCD'...]; [$alpha::length -> lexicalPermutations -> '$alpha($)...;' ] -> !OUT::write

Output:

That algorithm can also be written from the bottom up to produce an infinite stream of sets of larger and larger permutations, until we stop

templates lexicalPermutations2
def N: $; [[1]] -> # when <[<[]($N)>]> do $... ! otherwise def tails:$;
[1..$tails(1)::length+1 -> $$def first: ; tails... -> [first, ... -> \(when <first..> do +1! otherwise !$$] ! \)] -> # end lexicalPermutations2 [$alpha::length -> lexicalPermutations2 -> '$alpha($)...;' ] -> !OUT::write

Output:

The solutions above create a lot of new arrays at various stages. We can also use mutable state and just emit a copy for each generated solution.

templates perms
templates findPerms
when <[email protected]::length..> do [email protected] !
otherwise
def index: $; [email protected]::length -> $$@perms([, index]): [email protected]([index, ])...; index + 1 -> findPerms !$$ ! @perms([last,$index..last-1]): [email protected]($index..last)...; end findPerms @: [1..$];
1 -> findPerms !
end perms

def alpha: ['ABCD'...];
[4 -> perms -> '$alpha($)...;' ] -> !OUT::write

Output:

## Tcl

Library: Tcllib (Package: struct::list)
package require struct::list

# Make the sequence of digits to be permuted
set n [lindex $argv 0] for {set i 1} {$i <= $n} {incr i} {lappend sequence$i}

# Iterate over the permutations, printing as we go
struct::list foreachperm p $sequence { puts$p
}

Testing with tclsh listPerms.tcl 3 produces this output:

1 2 3
1 3 2
2 1 3
2 3 1
3 1 2
3 2 1

## True BASIC

Translation of: Liberty BASIC
SUB SWAP(vb1, vb2)
LET temp = vb1
LET vb1 = vb2
LET vb2 = temp
END SUB

LET n = 4
DIM a(4)
DIM c(4)

FOR i = 1 TO n
LET a(i) = i
NEXT i
PRINT

DO
FOR i = 1 TO n
PRINT a(i);
NEXT i
PRINT
LET i = n
DO
LET i = i - 1
LOOP UNTIL (i = 0) OR (a(i) < a(i + 1))
LET j = i + 1
LET k = n
DO WHILE j < k
CALL SWAP (a(j), a(k))
LET j = j + 1
LET k = k - 1
LOOP
IF i > 0 THEN
LET j = i + 1
DO WHILE a(j) < a(i)
LET j = j + 1
LOOP
CALL SWAP (a(i), a(j))
END IF
LOOP UNTIL i = 0
END

## Ursala

In practice there's no need to write this because it's in the standard library.

#import std

permutations =

~&itB^?a( # are both the input argument list and its tail non-empty?
@ahPfatPRD *= refer ^C( # yes, recursively generate all permutations of the tail, and for each one
~&a, # insert the head at the first position
~&ar&& ~&arh2falrtPXPRD), # if the rest is non-empty, recursively insert at all subsequent positions
~&aNC) # no, return the singleton list of the argument

test program:

#cast %nLL

test = permutations <1,2,3>
Output:
<
<1,2,3>,
<2,1,3>,
<2,3,1>,
<1,3,2>,
<3,1,2>,
<3,2,1>>

## VBA

Translation of: Pascal
Public Sub Permute(n As Integer, Optional printem As Boolean = True)
'Generate, count and print (if printem is not false) all permutations of first n integers

Dim P() As Integer
Dim t As Integer, i As Integer, j As Integer, k As Integer
Dim count As Long
Dim Last As Boolean

If n <= 1 Then

Debug.Print "Please give a number greater than 1"
Exit Sub

End If

'Initialize
ReDim P(n)

For i = 1 To n
P(i) = i
Next

count = 0
Last = False

Do While Not Last
'print?
If printem Then

For t = 1 To n
Debug.Print P(t);
Next

Debug.Print

End If

count = count + 1

Last = True
i = n - 1

Do While i > 0

If P(i) < P(i + 1) Then

Last = False
Exit Do

End If

i = i - 1
Loop

j = i + 1
k = n

While j < k
' Swap p(j) and p(k)
t = P(j)
P(j) = P(k)
P(k) = t
j = j + 1
k = k - 1
Wend

j = n

While P(j) > P(i)
j = j - 1
Wend

j = j + 1
'Swap p(i) and p(j)
t = P(i)
P(i) = P(j)
P(j) = t
Loop 'While not last

Debug.Print "Number of permutations: "; count

End Sub
Sample dialogue:
permute 1
give a number greater than 1!
permute 2
1  2
2  1
Number of permutations:  2
permute 4
1  2  3  4
1  2  4  3
1  3  2  4
1  3  4  2
1  4  2  3
1  4  3  2
2  1  3  4
2  1  4  3
2  3  1  4
2  3  4  1
2  4  1  3
2  4  3  1
3  1  2  4
3  1  4  2
3  2  1  4
3  2  4  1
3  4  1  2
3  4  2  1
4  1  2  3
4  1  3  2
4  2  1  3
4  2  3  1
4  3  1  2
4  3  2  1
Number of permutations:  24
permute 10,False
Number of permutations:  3628800

## VBScript

A recursive implementation. Arrays can contain anything, I stayed with with simple variables. (Elements could be arrays but then the printing routine should be recursive...)

'permutation ,recursive
a=array("Hello",1,True,3.141592)
cnt=0
perm a,0
wscript.echo vbcrlf &"Count " & cnt

sub print(a)
s=""
for i=0 to ubound(a):
s=s &" " & a(i):
next:
wscript.echo s :
cnt=cnt+1 :
end sub
sub swap(a,b) t=a: a=b :b=t: end sub

sub perm(byval a,i)
if i=ubound(a) then print a: exit sub
for j= i to ubound(a)
swap a(i),a(j)
perm a,i+1
swap a(i),a(j)
next
end sub

Output

Count 24

## Wren

### Recursive

Translation of: Kotlin
var permute // recursive
permute = Fn.new { |input|
if (input.count == 1) return [input]
var perms = []
var toInsert = input[0]
for (perm in permute.call(input[1..-1])) {
for (i in 0..perm.count) {
var newPerm = perm.toList
newPerm.insert(i, toInsert)
}
}
return perms
}

var input = [1, 2, 3]
var perms = permute.call(input)
System.print("There are %(perms.count) permutations of %(input), namely:\n")
perms.each { |perm| System.print(perm) }
Output:
There are 6 permutations of [1, 2, 3], namely:

[1, 2, 3]
[2, 1, 3]
[2, 3, 1]
[1, 3, 2]
[3, 1, 2]
[3, 2, 1]

### Iterative, lexicographical order

Translation of: Go
Library: Wren-math

Output modified to follow the pattern of the recursive version.

import "/math" for Int

var input = [1, 2, 3]
var perms = [input]
var a = input.toList
var n = a.count - 1
for (c in 1...Int.factorial(n+1)) {
var i = n - 1
var j = n
while (a[i] > a[i+1]) i = i - 1
while (a[j] < a[i]) j = j - 1
var t = a[i]
a[i] = a[j]
a[j] = t
j = n
i = i + 1
while (i < j) {
t = a[i]
a[i] = a[j]
a[j] = t
i = i + 1
j = j - 1
}
}
System.print("There are %(perms.count) permutations of %(input), namely:\n")
perms.each { |perm| System.print(perm) }
Output:
There are 6 permutations of [1, 2, 3], namely:

[1, 2, 3]
[1, 3, 2]
[2, 1, 3]
[2, 3, 1]
[3, 1, 2]
[3, 2, 1]

### Library based

Library: Wren-perm
import "./perm" for Perm

var a = [1, 2, 3]
System.print(Perm.list(a)) // not lexicographic
System.print()
System.print(Perm.listLex(a)) // lexicographic
Output:
[[1, 2, 3], [1, 3, 2], [2, 1, 3], [2, 3, 1], [3, 2, 1], [3, 1, 2]]

[[1, 2, 3], [1, 3, 2], [2, 1, 3], [2, 3, 1], [3, 1, 2], [3, 2, 1]]

## XPL0

code ChOut=8, CrLf=9;
def N=4; \number of objects (letters)
char S0, S1(N);

proc Permute(D); \Display all permutations of letters in S0
int D; \depth of recursion
int I, J;
[if D=N then
[for I:= 0 to N-1 do ChOut(0, S1(I));
CrLf(0);
return;
];
for I:= 0 to N-1 do
[for J:= 0 to D-1 do \check if object (letter) already used
if S1(J) = S0(I) then J:=100;
if J<100 then
[S1(D):= S0(I); \object (letter) not used so append it
Permute(D+1); \recurse next level deeper
];
];
];

[S0:= "rose "; \N different objects (letters)
Permute(0); \(space char avoids MSb termination)
]

Output:

rose
roes
rsoe
rseo
reos
reso
orse
ores
osre
oser
oers
oesr
sroe
sreo
sore
soer
sero
seor
eros
erso
eors
eosr
esro
esor

## Yabasic

Translation of: Liberty BASIC
n = 4
dim a(n), c(n)

for j = 1 to n : a(j) = j : next j

repeat
for i = 1 to n: print a(i);: next: print
i = n
repeat
i = i - 1
until (i = 0) or (a(i) < a(i+1))
j = i + 1
k = n
while j < k
tmp = a(j) : a(j) = a(k) : a(k) = tmp
j = j + 1
k = k - 1
wend
if i > 0 then
j = i + 1
while a(j) < a(i)
j = j + 1
wend
tmp = a(j) : a(j) = a(i) : a(i) = tmp
endif
until i = 0
end

## zkl

Using the solution from task Permutations by swapping#zkl:

zkl: Utils.Helpers.permute("rose").apply("concat")
L("rose","roes","reos","eros","erso","reso","rseo","rsoe","sroe","sreo",...)

zkl: Utils.Helpers.permute("rose").len()
24

zkl: Utils.Helpers.permute(T(1,2,3,4))
L(L(1,2,3,4),L(1,2,4,3),L(1,4,2,3),L(4,1,2,3),L(4,1,3,2),L(1,4,3,2),L(1,3,4,2),L(1,3,2,4),...)