Sorting algorithms/Cocktail sort

Sorting algorithms/Cocktail sort
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Sorting Algorithm
This is a sorting algorithm.   It may be applied to a set of data in order to sort it.     For comparing various sorts, see compare sorts.   For other sorting algorithms,   see sorting algorithms,   or:

O(n logn) sorts

Heap sort | Merge sort | Patience sort | Quick sort

O(n log²n) sorts
Shell Sort

O(n²) sorts
Bubble sort | Cocktail sort | Cocktail sort with shifting bounds | Comb sort | Cycle sort | Gnome sort | Insertion sort | Selection sort | Strand sort

other sorts
Bead sort | Bogo sort | Common sorted list | Composite structures sort | Custom comparator sort | Counting sort | Disjoint sublist sort | External sort | Jort sort | Lexicographical sort | Natural sorting | Order by pair comparisons | Order disjoint list items | Order two numerical lists | Object identifier (OID) sort | Pancake sort | Quickselect | Permutation sort | Radix sort | Ranking methods | Remove duplicate elements | Sleep sort | Stooge sort | [Sort letters of a string] | Three variable sort | Topological sort | Tree sort

The cocktail sort is an improvement on the Bubble Sort. The improvement is basically that values "bubble" both directions through the array, because on each iteration the cocktail sort bubble sorts once forwards and once backwards. Pseudocode for the algorithm (from the wikipedia):

function cocktailSort( A : list of sortable items )
 do
   swapped := false
   for each i in 0 to length( A ) - 2 do
     if A[ i ] > A[ i+1 ] then // test whether the two 
                               // elements are in the wrong 
                               // order
       swap( A[ i ], A[ i+1 ] ) // let the two elements
                                // change places
       swapped := true;
   if swapped = false then
     // we can exit the outer loop here if no swaps occurred.
     break do-while loop;
   swapped := false
   for each i in length( A ) - 2 down to 0 do
     if A[ i ] > A[ i+1 ] then
       swap( A[ i ], A[ i+1 ] )
       swapped := true;
 while swapped; // if no elements have been swapped, 
                // then the list is sorted

Ada

<lang Ada>with Ada.Text_Io; use Ada.Text_Io;

procedure Cocktail_Sort_Test is

  procedure Cocktail_Sort (Item : in out String) is
     procedure Swap(Left, Right : in out Character) is
        Temp : Character := Left;
     begin
        Left := Right;
        Right := Temp;
     end Swap;
     Swapped : Boolean := False;
  begin
     loop
        for I in 1..Item'Last - 1 loop
           if Item(I) > Item(I + 1) then
              Swap(Item(I), Item(I + 1));
              Swapped := True;
           end if;
        end loop;
        if not Swapped then
           for I in reverse 1..Item'Last - 1 loop
              if Item(I) > Item(I + 1) then
                 Swap(Item(I), Item(I + 1));
                 Swapped := True;
              end if;
           end loop;
        end if;
        exit when not Swapped;
        Swapped := False;
     end loop;
  end Cocktail_Sort;
  Data : String := "big fjords vex quick waltz nymph";

begin

  Put_Line(Data);
  Cocktail_Sort(Data);
  Put_Line(Data);

end Cocktail_Sort_Test;</lang>

ALGOL 68

<lang algol68>MODE DATA = CHAR; PROC swap = (REF DATA a,b)VOID:(

 DATA tmp:=a; a:=b; b:=tmp

);

PROC cocktail sort = (REF[]DATA a)VOID: (

 WHILE
   BOOL swapped := FALSE;
   FOR i FROM LWB a TO UPB a - 1 DO
     IF a[ i ] > a[ i + 1 ] THEN # test whether the two elements are in the wrong order #
       swap( a[ i ], a[ i + 1 ] ); # let the two elements change places #
       swapped := TRUE
     FI
   OD;
   IF NOT swapped THEN
     # we can exit the outer loop here if no swaps occurred. #
     break do while loop
   FI;
   swapped := FALSE;
   FOR i FROM UPB a - 1 TO LWB a DO
     IF a[ i ] > a[ i + 1 ] THEN
       swap( a[ i ], a[ i + 1 ] );
       swapped := TRUE
     FI
   OD;

1. WHILE # swapped # if no elements have been swapped, then the list is sorted #

 DO SKIP OD;
 break do while loop: SKIP

);

[32]CHAR data := "big fjords vex quick waltz nymph"; cocktail sort(data); print(data)</lang>

Output:

     abcdefghiijklmnopqrstuvwxyz

Alternatively - when the data records are large - the data can be manipulated indirectly, thus removing the need to actually swap large chunks of memory as only addresses are swapped. <lang algol68>MODE DATA = REF CHAR; PROC swap = (REF DATA a,b)VOID:(

 DATA tmp:=a; a:=b; b:=tmp

);

PROC (REF[]DATA a)VOID cocktail sort;

[32]CHAR data := "big fjords vex quick waltz nymph"; [UPB data]DATA ref data; FOR i TO UPB data DO ref data[i] := data[i] OD; cocktail sort(ref data); FOR i TO UPB ref data DO print(ref data[i]) OD; print(new line); print((data))</lang>

Output:

     abcdefghiijklmnopqrstuvwxyz
big fjords vex quick waltz nymph

The above two routines both scan the entire width of the array, in both directions, even though the first and last elements of each sweep had already reached their final destination during the previous pass. The solution is to zig-zag, but have the sweeps shorten and converge on the centre element. This reduces the number of comparisons required by about 50%. <lang algol68>PROC odd even sort = (REF []DATA a)VOID: (

 FOR offset FROM 0 DO
   BOOL swapped := FALSE;
   FOR i FROM LWB a + offset TO UPB a - 1 - offset DO
     IF a[ i ] > a[ i + 1 ] THEN # test whether the two elements are in the wrong order #
       swap( a[ i ], a[ i + 1 ] ); # let the two elements change places #
       swapped := TRUE
     FI
   OD;
 # we can exit the outer loop here if no swaps occurred. #
   IF NOT swapped THEN break do od loop FI;
   swapped := FALSE;
   FOR i FROM UPB a - 1 - offset - 1 BY - 1 TO LWB a + offset DO
     IF a[ i ] > a[ i + 1 ] THEN
       swap( a[ i ], a[ i + 1 ] );
       swapped := TRUE
     FI
   OD;
 # if no elements have been swapped, then the list is sorted #
   IF NOT swapped THEN break do od loop FI;
 OD;
 break do od loop: SKIP

);</lang>

AutoHotkey

contributed by Laszlo on the ahk forum <lang AutoHotkey>MsgBox % CocktailSort("") MsgBox % CocktailSort("xxx") MsgBox % CocktailSort("3,2,1") MsgBox % CocktailSort("dog,000000,xx,cat,pile,abcde,1,cat,zz,xx,z")

CocktailSort(var) {  ; SORT COMMA SEPARATED LIST

  StringSplit array, var, `,            ; make array
  i0 := 1, i1 := array0                 ; start, end

  Loop {                                ; break when sorted
    Changed =
    Loop % i1-- -i0 {                   ; last entry will be in place
      j := i0+A_Index, i := j-1
      If (array%j% < array%i%)          ; swap?
        t := array%i%, array%i% := array%j%, array%j% := t
       ,Changed = 1                     ; change has happened
    }
    IfEqual Changed,, Break

    Loop % i1-i0++ {                    ; first entry will be in place
      i := i1-A_Index, j := i+1
      If (array%j% < array%i%)          ; swap?
        t := array%i%, array%i% := array%j%, array%j% := t
       ,Changed = 1                     ; change has happened
    }
    IfEqual Changed,, Break
  }

  Loop % array0                         ; construct string from sorted array
    sorted .= "," . array%A_Index%
  Return SubStr(sorted,2)               ; drop leading comma

}</lang>

AWK

Sort the standard input and print it to standard output <lang awk>{

 line[NR] = $0

} END { # sort it with cocktail sort

 swapped = 0
 do {
   for(i=1; i < NR; i++) {
     if ( line[i] > line[i+1] ) {

t = line[i] line[i] = line[i+1] line[i+1] = t swapped = 1

     }
   }
   if ( swapped == 0 ) break
   swapped = 0
   for(i=NR-1; i >= 1; i--) {
     if ( line[i] > line[i+1] ) {

t = line[i] line[i] = line[i+1] line[i+1] = t swapped = 1

     }
   }
 } while ( swapped == 1 )
 #print it
 for(i=1; i <= NR; i++) {
   print line[i]
 }

}</lang>

C

<lang c>#include <stdio.h>

1. include <stdbool.h>

1. define COCKTSORT \

if ( a[i] > a[i+1] ) { \

 int temp = a[i];				\
 a[i] = a[i+1];				\
 a[i+1] = temp;				\
 swapped = true;				\

}

void cocktailsort(int *a, unsigned int l) {

 bool swapped = false;
 int i;

 do {
   for(i=0; i < (l-1); i++) {
     COCKTSORT;
   }
   if ( ! swapped ) break;
   swapped = false;
   for(i= l - 2; i >= 0; i--) {
     COCKTSORT;
   }
 } while(swapped);

}</lang> <lang c>int array[10] = { 5, -1, 101, -4, 0, 1, 8, 6, 2, 3 };

int main() {

 int i;

 cocktailsort(array, 10);
 for(i=0; i < 10; i++) {
   printf("%d\n", array[i]);
 }

}</lang>

C#

<lang csharp>public static void cocktailSort(int[] A)

   {
       bool swapped;
       do
       {
           swapped = false;
           for (int i = 0; i <= A.Length - 2; i++)
           {
               if (A[i] > A[i + 1])
               {
                   //test whether the two elements are in the wrong order
                   int temp = A[i];
                   A[i] = A[i + 1];
                   A[i + 1] = temp;
                   swapped = true;
               }
           }
           if (!swapped)
           {
               //we can exit the outer loop here if no swaps occurred.
               break;
           }
           swapped = false;
           for (int i = A.Length - 2; i >= 0; i--)
           {
               if (A[i] > A[i + 1])
               {
                   int temp = A[i];
                   A[i] = A[i + 1];
                   A[i + 1] = temp;
                   swapped = true;
               }
           }
           //if no elements have been swapped, then the list is sorted
       } while (swapped);
   }</lang>

Common Lisp

This version works on lists and vectors alike. The vector implementation is coded directly. The list version uses an intermediate vector.

<lang lisp>(defun cocktail-sort-vector (vector predicate &aux (len (length vector)))

 (labels ((scan (start step &aux swapped)
            (loop for i = start then (+ i step) while (< 0 i len) do
              (when (funcall predicate (aref vector i)
                                       (aref vector (1- i)))
                (rotatef (aref vector i)
                         (aref vector (1- i)))
                (setf swapped t)))
            swapped))
   (loop while (and (scan 1         1)
                    (scan (1- len) -1))))
 vector)

(defun cocktail-sort (sequence predicate)

 (etypecase sequence
   (vector (cocktail-sort-vector sequence predicate))
   (list (map-into sequence 'identity
                   (cocktail-sort-vector (coerce sequence 'vector)
                                         predicate)))))</lang>

D

This is generic solution based on templates. Main function is quite similar to provided pseudo-code. <lang D>import tango.io.Stdout; import tango.core.Variant; import tango.core.Traits;

// objects must have opIndex method template GetItemType(T) { alias ReturnTypeOf!(T.opIndex) GetItemType; } // specialization for arrays template GetItemType(T : T[]) { alias T GetItemType; }

void cocktailSort(T)(T elements) {

   static assert (isArray!(T) || isStaticArray!(T) || isObject!(T), "array or object required");

   alias GetItemType!(T) _itemT;
   bool swapped;

   void swap(T a, uint pos) {
       _itemT temp = a[pos]; a[pos] = a[pos+1]; a[pos+1] = temp; swapped = true;
   }

   do {
       swapped = false;
       foreach (idx, ref elem; elements[0 .. elements.length-1]) {
           if (elem > elements[idx+1])
               swap (elements, idx);
       }
       if (!swapped) break;
       swapped = false;
       foreach_reverse (idx, ref elem; elements[0 .. elements.length-1]) {
           if (elem > elements[idx+1])
               swap (elements, idx);
       }
   } while(swapped);

}</lang>Sample usage:<lang D>class SampleContainer {

   char[][] data;

public:

   this () {
       data ~= "John";
       data ~= "Kate";
       data ~= "Alice";
       data ~= "Joe";
       data ~= "Jane";
   }
   char[] opIndex(uint pos) { return data[pos]; }
   char[] opIndexAssign(char[] s, uint pos) { return (data[pos] = s); }
   char[][] opSlice(uint a, uint b) { return data[a..b]; }
   uint length() { return data.length; }
   char[] toString() {
       char[] ret = "[";
       foreach (elem; data) ret ~= elem ~ ", ";
       return ret ~ "]";
   }

}

void main() {

   auto y = new SampleContainer;
   auto x =  [5, 1, 7, 3, 6, 4, 2 ];
   
   cocktailSort(x);
   Stdout (x).newline;
   cocktailSort(y);
   Stdout (y).newline;

}</lang>

Output:

[ 1, 2, 3, 4, 5, 6, 7 ]
[Alice, Jane, Joe, John, Kate, ]

E

<lang e>/** Cocktail sort (in-place) */ def cocktailSort(array) {

   def swapIndexes := 0..(array.size() - 2)
   def directions := [swapIndexes, swapIndexes.descending()]
   while (true) {
       for direction in directions {
           var swapped := false
           for a ? (array[a] > array[def b := a + 1]) in direction {
               def t    := array[a]
               array[a] := array[b]
               array[b] := t
               swapped  := true
           }
           if (!swapped) { return }
       }
   }

}</lang>

Note that this solution contains no repeated code to handle the forward and reverse passes.

Fortran

Works with: Fortran version 90 and later

<lang fortran>PROGRAM COCKTAIL

 IMPLICIT NONE

 INTEGER :: intArray(10) = (/ 4, 9, 3, -2, 0, 7, -5, 1, 6, 8 /)

 WRITE(*,"(A,10I5)") "Unsorted array:", intArray
 CALL Cocktail_sort(intArray)
 WRITE(*,"(A,10I5)") "Sorted array  :", intArray
 

CONTAINS

 SUBROUTINE Cocktail_sort(a)
   INTEGER, INTENT(IN OUT) :: a(:)
   INTEGER :: i, bottom, top, temp 
   LOGICAL :: swapped

   bottom = 1
   top = SIZE(a) - 1
   DO WHILE (bottom < top )
      swapped = .FALSE.
      DO i = bottom, top
         IF (array(i) > array(i+1)) THEN
             temp = array(i)
             array(i) = array(i+1)
             array(i+1) = temp
             swapped = .TRUE.
         END IF
      END DO
      IF (.NOT. swapped) EXIT
      DO i = top, bottom + 1, -1
         IF (array(i) < array(i-1)) THEN
             temp = array(i)
             array(i) = array(i-1)
             array(i-1) = temp
             swapped = .TRUE.
         END IF
      END DO
      IF (.NOT. swapped) EXIT
      bottom = bottom + 1
      top = top - 1
   END DO
 END SUBROUTINE Cocktail_sort

END PROGRAM COCKTAIL</lang>

Haskell

<lang haskell>cocktailSort :: Ord a => [a] -> [a] cocktailSort l

 | not swapped1 = l
 | not swapped2 = reverse $ l1
 | otherwise    = cocktailSort l2
 where (swapped1, l1) = swappingPass (>) (False, []) l
       (swapped2, l2) = swappingPass (<) (False, []) l1

       swappingPass :: Ord a => (a -> a -> Bool) -> (Bool, [a]) -> [a] -> (Bool, [a])
       swappingPass op (swapped, l) (x1 : x2 : xs)
         | op x1 x2  = swappingPass op (True,    x2 : l) (x1 : xs)
         | otherwise = swappingPass op (swapped, x1 : l) (x2 : xs)
       swappingPass _  (swapped, l) [x] = (swapped, x : l)
       swappingPass _  pair         []  = pair</lang>

J

<lang j>bigToLeft=: (([ (>. , <.) {.@]) , }.@])/ smallToLeft=: (([ (<. , >.) {.@]) , }.@])/ cocktailSort=: |. @: (|. @: smallToLeft @: |. @: bigToLeft ^:_)</lang>

Test run:

<lang j>  ?. 10 $ 10 4 6 8 6 5 8 6 6 6 9

  cocktailSort ?. 10 $ 10

4 5 6 6 6 6 6 8 8 9</lang>

As is usual with J, /:~ is the preferred method of sorting in practice.

Java

This algorithm sorts in place. Call it with a copy of the array to preserve the unsorted order. <lang java>public static void cocktailSort( int[] A ){ boolean swapped; do{ swapped = false; for (int i =0; i<= A.length - 2;i++){ if (A[ i ] > A[ i + 1 ]) { //test whether the two elements are in the wrong order int temp = A[i]; A[i] = A[i+1]; A[i+1]=temp; swapped = true; } } if (!swapped) { //we can exit the outer loop here if no swaps occurred. break; } swapped = false; for (int i= A.length - 2;i>=0;i--){ if (A[ i ] > A[ i + 1 ]){ int temp = A[i]; A[i] = A[i+1]; A[i+1]=temp; swapped = true; } } //if no elements have been swapped, then the list is sorted } while (swapped); }</lang>

MAXScript

<lang maxscript>fn cocktailSort arr = (

   local swapped = true
   while swapped do
   (
       swapped = false
       for i in 1 to (arr.count-1) do
       (
           if arr[i] > arr[i+1] then
           (
               swap arr[i] arr[i+1]
               swapped = true
           )
       )
       if not swapped then exit			
       for i in (arr.count-1) to 1 by -1 do
       (
           if arr[i] > arr[i+1] then
           (
               swap arr[i] arr[i+1]
               swapped = true
           )
       )
   )
   return arr

)</lang>

OCaml

<lang ocaml>let swap a i j =

 let tmp = a.(i) in
 a.(i) <- a.(j);
 a.(j) <- tmp;

let cocktail_sort a =

 let begin_ = ref(-1)
 and end_ = ref(Array.length a - 2) in
 let swapped = ref true in
 try while !swapped do
   swapped := false;
   incr begin_;
   for i = !begin_ to !end_ do
     if a.(i) > a.(i+1) then begin
       swap a (i) (i+1);
       swapped := true;
     end;
   done;
   if !swapped = false then raise Exit;
   swapped := false;
   decr end_;
   for i = !end_ downto !begin_ do
     if a.(i) > a.(i+1) then begin
       swap a (i) (i+1);
       swapped := true
     end;
   done;
 done with Exit -> ()

let () =

 let a = [| 3; 7; 4; 9; 6; 1; 8; 5; 2; |] in
 cocktail_sort a;
 Array.iter (Printf.printf " %d") a;
 print_newline();

</lang>

outputs:

1 2 3 4 5 6 7 8 9

Octave

<lang octave>function sl = cocktailsort(l)

 swapped = true;
 while(swapped)
   swapped = false;
   for i = 1:(length(l)-1)
     if ( l(i) > l(i+1) )

t = l(i); l(i) = l(i+1); l(i+1) = t; swapped = true;

     endif
   endfor
   if ( !swapped )
     break;
   endif
   swapped = false;
   for i = (length(l)-1):-1:1
     if ( l(i) > l(i+1) )

t = l(i); l(i) = l(i+1); l(i+1) = t; swapped = true;

     endif      
   endfor
 endwhile
 sl = l;

endfunction</lang>

<lang octave>s = cocktailsort([5, -1, 101, -4, 0, \ 1, 8, 6, 2, 3 ]); disp(s);</lang>

Perl

<lang perl>use strict; use warnings;

my @B=qw(t h e q u i c k b r o w n f o x j u m p s o v e r t h e l a z y d o g); print "@B\n"; my @C=cocktailSort(@B); print "@C\n";

1. 1. 1. 1. 1. 1. 1. 1. 1. 1. 1. 1. 1. 1. 1. 1. 1. 1. 1. cocktailSort #####################

sub cocktailSort { #( A : list of sortable items ) defined as:

 my @A = @_;
 my $swapped = 1;
 while ($swapped == 1) {
   $swapped = 0;
   for (my $i=0; $i<($#A-1); $i+=1) {

     if ($A[$i] gt $A[$i+1]) { # test whether the two 
                           # elements are in the wrong 
                           # order

        ($A[$i+1], $A[$i])=($A[$i], $A[$i+1]); # let the two elements
                                               # change places
       $swapped = 1;
     } 
   }
   if ($swapped == 0) {
     # we can exit the outer loop here if no swaps occurred.
     print "no more swaps"; 
   }
   else {
   $swapped = 0;
   for (my $i=($#A-1); $i>0 ; $i-=1) {

     if($A[$i] gt $A[$i+1]) {

       ($A[$i+1], $A[$i])=($A[$i], $A[$i+1]);
       $swapped = 1;
     }
   }
   }

1. if no elements have been swapped,
2. then the list is sorted

 }

return (@A);

1. end sub

}</lang>

Python

This implementation takes advantage of the identical processing of the two for loops and that a range is a first-class object in Python.<lang python>def cocktailSort(A):

   up = range(len(A)-1)
   while True:
       for indices in (up, reversed(up)):
           swapped = False
           for i in indices:
               if A[i] > A[i+1]:  
                   A[i], A[i+1] =  A[i+1], A[i]
                   swapped = True
           if not swapped:
               return</lang>

Usage: <lang python>test1 = [7, 6, 5, 9, 8, 4, 3, 1, 2, 0] cocktailSort(test1) print test1

1. >>> [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

test2=list('big fjords vex quick waltz nymph') cocktailSort(test2) print str.join(, test2)

1. >>> abcdefghiijklmnopqrstuvwxyz</lang>

R

<lang R>cocktailsort <- function(x) {

  lenx <- length(x)
  repeat
  {
     swapped <- FALSE
     for(i in 1:(lenx-1))
     {
        if(x[i] > x[i+1])
        {
           temp <- x[i]
           x[i] <- x[i+1]
           x[i+1] <- temp
           swapped <- TRUE
        }     
     }
     if(!swapped) break
     
     swapped <- FALSE
     for(i in (lenx-1):1)
     {
        if(x[i] > x[i+1])
        {
           temp <- x[i]
           x[i] <- x[i+1]
           x[i+1] <- temp
           swapped <- TRUE
        }     
     }
     if(!swapped) break
  }  
  x 

}

print(cocktailsort(c(5, -1, 101, -4, 0, 1, 8, 6, 2, 3)))</lang>

Ruby

<lang ruby>class Array

 def cocktailsort!
   begin
     swapped = false
     0.upto(length - 2) do |i|
       if self[i] > self[i + 1]
         self[i], self[i + 1] = self[i + 1], self[i]
         swapped = true
       end
     end
     break if not swapped
     
     swapped = false
     (length - 2).downto(0) do |i|
       if self[i] > self[i + 1]
         self[i], self[i + 1] = self[i + 1], self[i]
         swapped = true
       end
     end
   end while swapped
   self
 end

end ary = [7,6,5,9,8,4,3,1,2,0] ary.cocktailsort!

1. => [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]</lang>

Slate

<lang slate>s@(Sequence traits) cocktailSort [ |swapped|

 swapped: False. 
 s size <= 1 ifTrue: [^ s].
 [{0 to: s size - 2. s size - 2 downTo: 0}
   do: [|:range| range do: [|:index| (s at: index) > (s at: index + 1) ifTrue: [s swap: index with: index + 1. swapped: True]].
        swapped ifFalse: [^ s].
        swapped: False].
 ] loop

].</lang>

<lang slate>slate[1]> #( 10 9 8 7 6 0 -5) cocktailSort. {-5. 0. 6. 7. 8. 9. 10}</lang>

Smalltalk

Works with: GNU Smalltalk

<lang smalltalk>OrderedCollection extend [

 swap: indexA and: indexB [
   |t|
   t := self at: indexA.
   self at: indexA put: (self at: indexB).
   self at: indexB put: t
 ]
 cocktailSort [
   |swapped|
   [
     swapped := false.
     1 to: (self size - 1) do: [ :i |
       (self at: i) > (self at: (i+1)) ifTrue: [
         self swap: i and: (i+1).

swapped := true

       ]
     ].
     swapped ifFalse: [ ^ self ].
     swapped := false.
     (self size - 1) to: 1 by: -1 do: [ :i |
       (self at: i) > (self at: (i+1)) ifTrue: [
         self swap: i and: (i+1).

swapped := true

       ]
     ].
     swapped
   ] whileTrue: [ ].
   ^ self
 ]

].</lang>

<lang smalltalk>(#( 10 9 8 7 6 0 -5) asOrderedCollection cocktailSort) printNl.</lang>

Tcl

uses package struct::list from

Library: tcllib

to swap list elements

<lang tcl>package require Tcl 8.5 package require struct::list

proc cocktailsort {A} {

   set len [llength $A]
   set swapped true
   while {$swapped} {
       set swapped false
       for {set i 0} {$i < $len - 1} {incr i} {
           set j [expr {$i + 1}]
           if {[lindex $A $i] > [lindex $A $j]} {
               struct::list swap A $i $j
               set swapped true
           }
       }
       if { ! $swapped} {
           break
       }
       set swapped false
       for {set i [expr {$len - 2}]} {$i >= 0} {incr i -1} {
           set j [expr {$i + 1}]
           if {[lindex $A $i] > [lindex $A $j]} {
               struct::list swap A $i $j
               set swapped true
           }
       }
   }
   return $A

}

puts [cocktailsort {8 6 4 2 1 3 5 7 9}] ;# => 1 2 3 4 5 6 7 8 9</lang>

Ursala

The same function is used for the traversal in each direction, in one case parameterized by the given predicate and in the other by its negation. Lists are used rather than arrays. The fold combinator (=>) avoids explicit recursion. <lang Ursala>#import std

ctsort = ^=+ +^|(==?/~&l+ @r+ ~&x++ @x,^/~&)+ ("p". =><> ~&r?\~&C "p"?lrhPX/~&C ~&rhPlrtPCC)^~/not ~&</lang> test program: <lang Ursala>#cast %s

test = ctsort(lleq) 'mdfdguldxisgbxjtqkadfkslakwkyioukdledbig'</lang> output:

'aabbddddddeffgggiiijkkkkklllmoqsstuuwxxy'