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Generate random numbers without repeating a value

From Rosetta Code
Generate random numbers without repeating a value is a draft programming task. It is not yet considered ready to be promoted as a complete task, for reasons that should be found in its talk page.

Many puzzle games such as the 15 puzzle game need a way to randomize the order of the pieces. One way to do this is to create an array and fill it with random values, with each element's index in that array being its position. Unfortunately, most random number generators can produce the same value more than once, which in this case isn't what we want.


Task

Create a random number generator and have it output the numbers 1 through 20 (inclusive), in a random order. It cannot produce the same value more than once.

Or

Given the output of an existing random number generator that does produce repeated output, create a function that constrains the output to numbers 1 through 20 (inclusive), and no number is output more than once. (Technically it stops being "random" at that point, but that's beyond the scope of this task.) Try your best not to make the process take too long at runtime.

For the second version of the task, the random number generator itself need not be implemented; however you must specify its possible range of values before your constraint function is applied. (e.g "Assume the random number generator creates a value from 0 to 255, and values are allowed to repeat")

Related Tasks



Action![edit]

PROC PrintTable(BYTE ARRAY tab BYTE size)
BYTE i
 
FOR i=0 TO size-1
DO
PrintF("%B ",tab(i))
OD
PutE() PutE()
RETURN
 
PROC KnuthShuffle(BYTE ARRAY tab BYTE size)
BYTE i,j,tmp
 
i=size-1
WHILE i>0
DO
j=Rand(i)
tmp=tab(i)
tab(i)=tab(j)
tab(j)=tmp
i==-1
OD
RETURN
 
PROC Main()
DEFINE LEN="20"
BYTE ARRAY tab(LEN)
BYTE i
 
FOR i=1 TO LEN
DO
tab(i-1)=i
OD
FOR i=1 TO 5
DO
KnuthShuffle(tab,LEN)
PrintTable(tab,LEN)
OD
RETURN
Output:

Screenshot from Atari 8-bit computer

17 6 20 3 8 10 14 12 4 15 2 7 16 18 15 19 9 13 11

6 8 1 10 5 20 16 14 3 12 13 2 17 11 9 4 7 19 18 15

3 15 13 8 19 5 10 1 17 20 16 4 2 6 14 7 18 11 9 12

19 16 15 9 4 14 20 2 11 12 3 6 8 17 15 10 18 13 7

14 2 1 18 10 7 13 11 17 4 20 9 6 3 16 19 5 15 12 8


BASIC[edit]

BASIC256[edit]

Translation of: FreeBASIC
arraybase 1
for num = 1 to 5
call pRand()
next num
end
 
subroutine pRand()
dim randCheck(21)
nr = 1
do
aleat = int(rand * 20) + 1
if randCheck[aleat] = 1 then
continue do
else
randCheck[aleat] = 1
print aleat; " ";
end if
for n = 1 to randCheck[?]
if randCheck[nr] then nr += 1
next n
until nr = 21
print
end subroutine

QBasic[edit]

Translation of: FreeBASIC
DECLARE SUB pRand ()
 
RANDOMIZE TIMER
FOR num = 1 TO 5
pRand
NEXT num
END
 
SUB pRand
DIM randCheck(1 TO 21)
nr = 1
DO
aleat = INT(RND * 20) + 1
IF randCheck(aleat) <> 1 THEN
randCheck(aleat) = 1
PRINT aleat;
END IF
 
FOR n = 1 TO UBOUND(randCheck)
IF randCheck(nr) = 1 THEN nr = nr + 1
NEXT n
LOOP UNTIL nr = 21
PRINT
END SUB

F#[edit]

 
// Generate random numbers without repeating a value. Nigel Galloway: August 27th., 2021
MathNet.Numerics.Combinatorics.GeneratePermutation 20|>Array.map((+)1)|>Array.iter(printf "%d "); printfn ""
 
Output:
12 7 17 8 10 13 16 19 20 14 18 5 9 11 3 4 1 15 6 2

Factor[edit]

Generating a random permutation of 1..20:

Works with: Factor version 0.99 2021-06-02
USING: kernel math.combinatorics math.ranges prettyprint random
sequences ;
 
: random-permutation ( seq -- newseq )
[ length dup nPk random ] keep permutation ;
 
20 [1,b] random-permutation .
Output:
{ 7 10 12 9 5 8 20 14 18 4 13 3 17 16 19 6 15 1 2 11 }

Shuffling 1..20:

Works with: Factor version 0.99 2021-06-02
USING: math.ranges prettyprint random vectors ;
 
20 [1,b] >vector randomize .
Output:
V{ 20 7 8 17 18 1 15 13 12 10 3 14 19 2 5 9 16 11 6 4 }

Sampling 20 elements from 1..20:

Works with: Factor version 0.99 2021-06-02
USING: math.ranges prettyprint random ;
 
20 [1,b] 20 sample .
Output:
{ 12 3 16 13 1 9 8 11 5 19 15 18 17 20 10 4 7 14 6 2 }


FreeBASIC[edit]

Sub pRand
Dim As Integer randCheck(20), nr = 1
Do
Dim As Integer aleat = Int(Rnd * 20) + 1
If randCheck(aleat) = 1 Then
Continue Do
Else
randCheck(aleat) = 1
Print aleat;
End If
For n As Integer = 1 To Ubound(randCheck)
If randCheck(nr) = 1 Then nr += 1
Next n
Loop Until nr = 21
Print
End Sub
 
Randomize Timer
For num As Integer = 1 To 5
pRand()
Next num
Sleep
Output:
7 11 16 13 14 6 20 2 1 10 17 18 9 12 4 8 15 19 5 3
9 6 18 16 3 14 1 8 11 2 7 20 4 13 19 12 17 5 15 10
11 19 15 6 10 17 13 8 18 2 12 14 16 5 4 1 3 9 7 20
5 18 13 8 4 15 16 12 7 6 1 19 2 17 9 14 10 20 3 11
19 5 4 9 12 11 8 14 6 13 3 1 7 2 16 18 10 17 20 15


Go[edit]

Translation of: Nim

This uses Go's 'native' random number generator which internally uses a custom algorithm attributed to D P Mitchell and J A Reeds and can generate non-negative random integers in the 64-bit range.

package main
 
import (
"fmt"
"log"
"math/rand"
"time"
)
 
// Generates and prints all numbers within an inclusive range whose endpoints are
// non-negative 64-bit integers. The numbers are generated in random order with
// any repetitions being ignored.
func generate(from, to int64) {
if to < from || from < 0 {
log.Fatal("Invalid range.")
}
span := to - from + 1
generated := make([]bool, span) // all false by default, zero indexing
count := span
for count > 0 {
n := from + rand.Int63n(span) // upper endpoint is exclusive
if !generated[n-from] {
generated[n-from] = true
fmt.Printf("%2d ", n)
count--
}
}
fmt.Println()
}
 
func main() {
rand.Seed(time.Now().UnixNano())
 
// generate 5 sets say
for i := 1; i <= 5; i++ {
generate(1, 20)
}
}
Output:

Sample run:

16  7  5 11 10 12  1 19  9  2  4 14  6 18 17  8 20  3 13 15 
10  3  5  7 14  9 20  6 11  8 13 18  1 17 15 12  4  2 16 19 
12 14 16 11 15  2  8 13  3 19  6 17 18  4 10  5 20  1  7  9 
 4 11  9 17 14 16  2  7  6  1 12 20  8 15  5 13 10 18 19  3 
19 13  9  7  5 12 11 17  1  3 16  4 15 14 20  8  6 18  2 10 


Alternatively and far more efficiently, we can simply create a list of the required numbers and randomly shuffle them. Go has a standard library function for this which uses the Fisher-Yates (aka Knuth) shuffle.

package main
 
import (
"fmt"
"math/rand"
"time"
)
 
func main() {
rand.Seed(time.Now().UnixNano())
numbers := make([]int, 20)
for i := 0; i < 20; i++ {
numbers[i] = i + 1
}
for i := 1; i <= 5; i++ {
rand.Shuffle(20, func(i, j int) {
numbers[i], numbers[j] = numbers[j], numbers[i]
})
s := fmt.Sprintf("%2d ", numbers)
fmt.Println(s[1 : len(s)-2])
}
}
Output:
13 10 18  7  3  5 17  4  1 11 16 20  9 12 14  2 15 19  6  8
19 12 11  1  3 14  7 20  2 18  4 10  9  5  8  6 15 13 16 17
10  6 11  3  5 13 15  4 16 12  1 14 20  7  2 19  8 17  9 18
 4 14 17 15  1  6 12 11  2  3 19 10  9 18  7 13  8 20 16  5
13 12  8  3  9 17 14 10  6  2 11 20 19 18  4  7 16  1 15  5

Java[edit]

import java.util.*;
 
public class RandomShuffle {
public static void main(String[] args) {
Random rand = new Random();
List<Integer> list = new ArrayList<>();
for (int j = 1; j <= 20; ++j)
list.add(j);
Collections.shuffle(list, rand);
System.out.println(list);
}
}
Output:
[19, 15, 10, 6, 17, 13, 14, 9, 2, 20, 3, 18, 8, 16, 7, 12, 1, 4, 5, 11]

jq[edit]

Works with: jq

Works with gojq, the Go implementation of jq

In this entry, an external source of entropy is used to define a jq filter, `knuthShuffle`, so that the specific task can then be accomplished using the expression:

[range(1;21)] | knuthShuffle

In the following, a bash or bash-like scripting environment is assumed, and the jq command is assumed to be "jq".

 
< /dev/urandom tr -cd '0-9' | fold -w 1 | jq -MRcnr -f program.jq
 

program.jq

# Output: a prn in range(0;$n) where $n is `.`
def prn:
if . == 1 then 0
else . as $n
| ([1, (($n-1)|tostring|length)]|max) as $w
| [limit($w; inputs)] | join("") | tonumber
| if . < $n then . else ($n | prn) end
end;
 
def knuthShuffle:
length as $n
| if $n <= 1 then .
else {i: $n, a: .}
| until(.i == 0;
.i += -1
| (.i + 1 | prn) as $j
| .a[.i] as $t
| .a[.i] = .a[$j]
| .a[$j] = $t)
| .a
end;
 
# The task:
[range(1;21)] | knuthShuffle
Output:
4
11
3
8
1
9
16
6
5
7
12
17
15
19
10
20
18
2
13
14

Julia[edit]

Julia's Random module contains a function called `randperm(n::Integer)` which constructs a random permutation of integers from 1 to n.

using Random
@show randperm(20)
 
Output:
randperm(20) = [20, 2, 5, 6, 18, 14, 12,4, 13, 7, 15, 3, 19, 17, 1, 9, 16, 11, 10]

Nim[edit]

Translation of: Wren

Nim standard module random provides a PRNG based on xoroshiro128+ algorithm whose period is 2^128 − 1. It also provides the shuffle procedure to shuffle an array or a sequence using Knuth algorithm.

Here, we have defined a procedure which accepts a slice a..b as argument and returns a shuffled sequence of values from a to b. It uses the same algorithm as in Wren solution, i.e. a list to keep track of generated values.

import random
 
randomize()
 
proc generate(s: Slice[int]): seq[int] =
assert s.a <= s.b
var count = s.b - s.a + 1
var generated = newSeq[bool](count) # Initialized to false.
while count != 0:
let n = rand(s)
if not generated[n - s.a]:
generated[n - s.a] = true
result.add n
dec count
 
for i in 1..5:
echo generate(1..20)
Output:
@[11, 15, 13, 9, 10, 6, 14, 1, 16, 4, 20, 17, 5, 7, 2, 3, 8, 12, 19, 18]
@[11, 3, 15, 12, 10, 16, 6, 18, 4, 13, 14, 19, 1, 7, 2, 5, 9, 20, 17, 8]
@[16, 10, 8, 1, 2, 18, 19, 4, 5, 11, 14, 15, 3, 13, 9, 12, 7, 20, 17, 6]
@[4, 7, 1, 15, 11, 2, 10, 6, 19, 5, 12, 9, 14, 13, 17, 3, 18, 20, 8, 16]
@[10, 9, 15, 2, 17, 8, 3, 20, 18, 12, 11, 14, 16, 13, 4, 5, 6, 1, 7, 19]

Perl[edit]

Just shuffle...

#!/usr/bin/perl
 
use strict; # https://rosettacode.org/wiki/Generate_random_numbers_without_repeating_a_value
use warnings;
use List::Util qw( shuffle );
 
print "@{[ shuffle 1 .. 20 ]}\n" for 1 .. 5;
Output:
9 15 11 14 17 10 13 1 2 7 19 3 6 12 4 16 8 5 18 20
20 17 18 6 1 19 14 10 2 7 4 12 8 15 3 16 9 11 5 13
4 3 9 15 6 20 14 8 18 5 19 17 1 10 11 16 12 2 13 7
17 9 3 15 1 20 7 19 13 8 11 10 6 5 4 14 12 18 16 2
13 1 5 18 12 11 3 14 10 9 19 4 20 16 8 6 17 2 7 15


Phix[edit]

Trival use of standard builtins. Progressively filtering the output of rand(20) would gain nothing except wasted cycles. Normally I would use "with javascript_semantics", or equivalently just "with js", to explicitly specify/verify the code can be run on both the desktop and in a web browser, however here that somehow seems like overkill.

?shuffle(tagset(20))
Output:
{13,6,8,1,9,19,5,18,2,12,11,20,4,17,10,3,15,7,14,16}

Python[edit]

 
import random
 
print(random.sample(range(1, 21), 20))
 
Output:
[14, 15, 3, 18, 4, 11, 16, 10, 12, 20, 13, 1, 6, 7, 2, 17, 5, 9, 19, 8]

Quackery[edit]

As a dialogue in the Quackery shell.

Welcome to Quackery.

Enter "leave" to leave the shell.

/O> [] 20 times [ i^ 1+ join ]
... shuffle 
... echo
... 
[ 7 6 9 5 13 11 15 17 19 2 14 20 12 4 8 1 3 18 10 16 ]
Stack empty.

/O> leave
... 

Auf wiedersehen.

R[edit]

R makes this so easy that it feels like you've missed the point.

sample(20)

Raku[edit]

Raku has three distinct "random" functions built in. rand() for when you want some fraction between 0 and 1. roll() when you want to select elements from a collection with replacement (rolls of a die). And pick() for when you want to select some elements from a collection without replacement. (pick a card, any card, or two cards or 10 cards...). If you want to select all the elements in random order, just pick 'whatever'. Here we'll pick all from 1 to 20, 5 times using the repetition operator.

.put for (1..20).pick(*) xx 5
Sample output:
20 4 5 7 15 19 2 16 8 6 3 12 14 13 10 18 9 17 1 11
4 5 18 10 13 3 1 11 6 2 19 8 12 7 16 17 14 20 15 9
14 8 15 11 17 4 3 10 18 7 16 13 1 20 12 9 6 5 19 2
7 5 15 11 12 18 17 3 20 6 13 19 14 2 16 10 4 9 8 1
19 12 4 7 3 20 13 17 5 8 6 15 10 18 1 11 2 14 16 9

REXX[edit]

The REXX solution to this task is performed in essentially three parts:
: Part 1.     (The DO i   ...)   build a list of sequential integers.
: Part 2.     (The DO r   ...)   build an array of random integers, using the list as a selection template.
: Part 3.     (The DO o   ...)   display a grid of the random integers with title and formatting.

With the method/algorithm used herein,   there are   no   random numbers being discarded   (due to possible
duplicates)   because there cannot   be   any duplicates.

/*REXX program generates & displays a list of random integers (1 ──► N) with no repeats.*/
parse arg n cols seed . /*obtain optional argument from the CL.*/
if n=='' | n=="," then n= 20 /*Not specified? Then use the default.*/
if cols=='' | cols=="," then cols= 10 /* " " " " " " */
if datatype(seed, 'W') then call random ,,seed /*Specified? Then use the seed. */
w= 6
title= ' random integers (1 ──► ' n") with no repeats"
say ' index │'center(title, 1 + cols*(w+1) ) /*display the output title. */
say '───────┼'center("" , 1 + cols*(w+1), '─') /* " " " separator*/
a=
do i=1 for n; a= a i /*create a list of possible integers. */
end /*i*/ /*step through the (random) integers. */
pool= n
do r=1 for n;  ?= random(1, pool) /*obtain a random integer from the list*/
@.r= word(a, ?); a= delword(a, ?, 1) /*obtain random integer; del from pool.*/
pool= pool - 1 /*diminish size of the allowable pool. */
end /*r*/ /*step through the (random) integers. */
$=; idx= 1
do o=1 for n; x= @.o /*obtain a random integer from random @*/
$= $ right( x, w) /*add an integer to the output list. */
if o//cols\==0 then iterate /*have we populated a line of output? */
say center(idx, 7)'│' substr($, 2); $= /*display what we have so far (cols). */
idx= idx + cols /*bump the index count for the output*/
end /*j*/
 
if $\=='' then say center(idx, 7)"│" substr($, 2) /*possible show residual output.*/
say '───────┴'center("" , 1 + cols*(w+1), '─'); say
exit 0 /*stick a fork in it, we're all done. */
output   when using the default inputs:
 index │             random integers  (1 ──►  20)  with no repeats
───────┼───────────────────────────────────────────────────────────────────────
   1   │     20      7      5     12     11      6     19      8      4     10
  11   │      9     17     15     13      1     16      3     18     14      2
───────┴───────────────────────────────────────────────────────────────────────

Ring[edit]

 
see "working..." + nl
decimals(3)
time1 = clock()
for num = 1 to 5
pRand()
next
 
time2 = clock()
time3 = time2/1000 - time1/1000
see "Elapsed time = " + time3 + " s" + nl
see "done..." + nl
 
func pRand
randCheck = list(20)
while true
rnd = random(19)+1
if randCheck[rnd] = 1
loop
else
randCheck[rnd] = 1
see "" + rnd + " "
ok
nr = 1
for n = 1 to len(randCheck)
if randCheck[nr] = 1
nr++
ok
next
if nr = 21
see nl
exit
ok
end
 
Output:
working...
6 11 16 19 10 15 3 1 8 7 2 9 20 5 4 14 12 13 17 18 
7 20 2 15 8 5 9 13 17 19 1 6 4 16 11 18 3 12 10 14 
5 19 12 3 1 10 15 7 9 17 18 4 20 13 2 11 8 14 16 6 
11 10 17 1 5 19 15 4 18 9 20 12 13 6 3 2 7 8 16 14 
2 14 15 6 19 20 3 17 5 1 8 13 4 18 7 9 10 16 11 12 
Elapsed time = 0.008 s
done...

Ruby[edit]

nums = (1..20).to_a
5.times{ puts nums.shuffle.join(" ") }
Output:
2 9 19 12 7 18 17 13 5 6 20 10 14 4 1 8 11 15 3 16
18 6 9 5 17 14 2 13 7 16 4 11 15 10 3 8 12 19 1 20
2 16 7 12 3 10 13 17 20 18 11 14 5 15 1 19 9 6 4 8
10 14 5 15 8 1 7 12 16 6 18 4 9 3 11 20 19 17 13 2
2 16 13 12 6 18 14 4 15 7 9 10 8 11 19 5 17 1 3 20

Rust[edit]

// [dependencies]
// rand = "0.7.2"
 
fn main() {
use rand::seq::SliceRandom;
use rand::thread_rng;
let mut rng = thread_rng();
let mut v: Vec<u32> = (1..=20).collect();
v.shuffle(&mut rng);
println!("{:?}", v);
}
Output:
[11, 19, 1, 7, 15, 4, 13, 10, 16, 3, 2, 18, 20, 17, 9, 8, 5, 6, 12, 14]

Swift[edit]

var array = Array(1...20)
array.shuffle()
print(array)
Output:
[4, 19, 13, 8, 14, 6, 18, 20, 11, 16, 17, 7, 5, 9, 2, 15, 3, 1, 10, 12]

Wren[edit]

Library: Wren-fmt

This uses Wren's 'native' pseudo-random number generator which internally uses WELL512a and can generate random integers in the 32-bit range.

import "random" for Random
import "/fmt" for Fmt
 
var rand = Random.new()
 
// Generates and prints all numbers within an inclusive range whose endpoints are 32 bit integers.
// The numbers are generated in random order with any repetitions being ignored.
var generate = Fn.new { |r|
var generated = List.filled(r.to - r.from + 1, false) // zero indexing
while (generated.any { |g| !g }) {
var n = rand.int(r.from, r.to + 1) // upper endpoint is exclusive
if (!generated[n - r.from]) {
generated[n - r.from] = true
Fmt.write("$2d ", n)
}
}
System.print()
}
 
// generate 5 sets say
for (i in 1..5) generate.call(1..20)
Output:

Sample run:

 4 16 10  5  1  2  9 19  7 12 15 11 18  3 13 17 20 14  6  8 
16  1  9 11  8 10 19  5  4  6 17 20 12 15  3  7 14 18  2 13 
 5 15 13  1 17 19 16  2  7 12 18  8 14  6 20  9 10 11  3  4 
 9  6 20 16  2 14 19  1  7 18 11 12  4 15  5 17  3  8 10 13 
16  1  8 14  5 19  3  4 18 12 20  2 10  6 13 11  7 15  9 17 


Alternatively and far more efficiently, we can simply create a list of the required numbers and randomly shuffle them. Wren has a built-in function for this which uses the Fisher-Yates (aka Knuth) shuffle.

import "random" for Random
import "/fmt" for Fmt
 
var rand = Random.new()
var numbers = (1..20).toList
for (i in 1..5) {
rand.shuffle(numbers)
Fmt.print("$2d", numbers)
}
Output:
 3 19 16 12  7  5  9 10 15 13  6 11 20 14  8 18  4 17  1  2
15  1 18 14  4 20 11  2  6  3 12  5  7 10 16 17  9 13 19  8
19  6 14  1 13  2 18 20 11  8  5  3  9 12 15 17  4 16 10  7
16 15  5 10  1 13 17  6  8  9 20  3 14 11 18  2 19 12  4  7
17  6 10 13 20  5  3 11 18 12 16  2 14 15 19  9  8  1  4  7