Sattolo cycle

Sattolo cycle 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.

Task

Implement the   Sattolo cycle   for an integer array (or, if possible, an array of any type).

Sattolo cycle is use to shuffle an array ensuring each index is in a new position.

Related tasks

• Knuth shuffle

C#

<lang csharp>private static readonly Random Rand = new Random();

void sattoloCycle<T>(IList<T> items) {

   for (var i = items.Count; i-- > 1;) {
       int j = Rand.Next(i);
       var tmp = items[i];
       items[i] = items[j];
       items[j] = tmp;
   }

}</lang>

J

This task currently needs a better description. That said, this achieves the result of the Sattolo cycle:

<lang J> (?~ #)</lang>

Java

<lang Java>private static final Random rng = new Random();

void sattoloCycle(Object[] items) {

   for (int i = items.length; i-- > 1;) {
       int j = rng.nextInt(i);
       Object tmp = items[i];
       items[i] = items[j];
       items[j] = tmp;
   }

}</lang>

JavaScript

<lang JavaScript>function sattoloCycle(items) {

   for (var i = items.length; i--> 1;) {
       var j = Math.floor(Math.random() * i);
       var tmp = items[i];
       items[i] = items[j];
       items[j] = tmp;
   }

}</lang>

Perl 6

This modifies the array passed as argument, in-place.

<lang perl6>sub sattolo-cycle (@array) {

   for reverse 1 .. @array.end -> $i {
       my $j = (^$i).pick;
       @array[$j, $i] = @array[$i, $j];
   }

}</lang>

Python

Copied from Wikipedia:

<lang python>from random import randrange

def sattoloCycle(items):

   i = len(items)
   while i > 1:
       i = i - 1
       j = randrange(i)  # 0 <= j <= i-1
       items[j], items[i] = items[i], items[j]
   return</lang>

REXX

This REXX example uses a zero-based array;   the array elements can be of any type. <lang rexx>/*REXX program implements and displays a Sattolo shuffle for an array (of any type).*/ parse arg a; a=space(a) /*obtain optional arguments from the CL*/ if a= then a='-1 0 1 2 00 44 5 {6} 7 ~ 8 7.9 one two ¬¬ four +4 five six /\ [nine] Ace' say 'original:' a n=words(a) /*obtain the number of elements in list*/

          do j=0  for n;  @.j=word(a, j+1); end /*assign an element to the  @.  array. */

          do i=0  to  n-2;  j=random(i, n-1)    /*get a random integer between I & N-1.*/
          parse value  @.i  @.j  with  @.j  @.i /*swap two array elements, J is random.*/
          end   /*i*/

$=@.0 /*start with the first element in array*/

          do k=1  for n-1;  $=$  @.k;   end     /*append the next element in the array.*/

say ' Sattolo:' $ /*stick a fork in it, we're all done. */</lang>

output   when using the default input:

original: -1 0 1 2 00 44 5 {6} 7 ~ 8 7.9 one two ¬¬ four +4 five six /\ [nine] Ace
 Sattolo: 7 ~ {6} +4 44 5 00 7.9 two [nine] four one 0 -1 /\ ¬¬ five 8 Ace 1 2 six

TypeScript

<lang TypeScript>function sattoloCycle<T>(items: Array<T>): void {

   for (let i = items.length; i--> 1;) {
       const j = Math.floor(Math.random() * i);
       const tmp = items[i];
       items[i] = items[j];
       items[j] = tmp;
   }

}</lang>

zkl

<lang zkl>fcn sattoloCycle(list){ // in place

  foreach i in ([list.len()-1 .. 1,-1]){
     list.swap(i,(0).random(i));  # 0 <= j < i
  }
  list

}</lang> <lang zkl>sattoloCycle([0..9].walk().copy()).println(); sattoloCycle("this is a test".split()).println();</lang>

Output:

L(6,3,8,2,5,7,1,0,9,4)
L("test","this","is","a")