Knuth shuffle
You are encouraged to solve this task according to the task description, using any language you may know.
Implement the Knuth shuffle (aka the Fisher-Yates shuffle) for an integer array (or, if possible, an array of any type). The Knuth shuffle is used to create a random permutation of an array.
Ada
This implementation is a generic shuffle routine, able to shuffle an array of any type. <lang Ada> generic
type Element_Type is private; type Array_Type is array (Positive range <>) of Element_Type;
procedure Generic_Shuffle (List : in out Array_Type); </lang> <lang Ada> with Ada.Numerics.Discrete_Random;
procedure Generic_Shuffle (List : in out Array_Type) is
package Discrete_Random is new Ada.Numerics.Discrete_Random(Result_Subtype => Integer); use Discrete_Random; K : Integer; G : Generator; T : Element_Type;
begin
Reset (G);
for I in reverse List'Range loop
K := (Random(G) mod I) + 1;
T := List(I);
List(I) := List(K);
List(K) := T;
end loop;
end Generic_Shuffle; </lang> An example using Generic_Shuffle. <lang Ada> with Ada.Text_IO; with Generic_Shuffle;
procedure Test_Shuffle is
type Integer_Array is array (Positive range <>) of Integer;
Integer_List : Integer_Array
:= (1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18);
procedure Integer_Shuffle is new Generic_Shuffle(Element_Type => Integer,
Array_Type => Integer_Array);
begin
for I in Integer_List'Range loop
Ada.Text_IO.Put(Integer'Image(Integer_List(I)));
end loop;
Integer_Shuffle(List => Integer_List);
Ada.Text_IO.New_Line;
for I in Integer_List'Range loop
Ada.Text_IO.Put(Integer'Image(Integer_List(I)));
end loop;
end Test_Shuffle; </lang>
AutoHotkey
ahk forum: discussion <lang AutoHotkey>MsgBox % shuffle("1,2,3,4,5,6,7,8,9") MsgBox % shuffle("1,2,3,4,5,6,7,8,9")
shuffle(list) { ; shuffle comma separated list, converted to array
StringSplit a, list, `, ; make array (length = a0)
Loop % a0-1 {
Random i, A_Index, a0 ; swap item 1,2... with a random item to the right of it
t := a%i%, a%i% := a%A_Index%, a%A_Index% := t
}
Loop % a0 ; construct string from sorted array
s .= "," . a%A_Index%
Return SubStr(s,2) ; drop leading comma
}</lang>
BASIC
<lang qbasic> RANDOMIZE TIMER
DIM unShuffled(51) AS INTEGER DIM Shuffled(51) AS INTEGER DIM L0 AS LONG, card AS LONG
PRINT "before:" FOR L0 = 0 TO 51
unShuffled(L0) = L0 PRINT LTRIM$(STR$(unShuffled(L0))); " ";
NEXT
FOR L0 = 51 TO 0 STEP -1
card = INT(RND * (L0 + 1)) Shuffled(L0) = unShuffled(card) IF card <> L0 THEN unShuffled(card) = unShuffled(L0)
NEXT
PRINT : PRINT : PRINT "after:" FOR L0 = 0 TO 51
PRINT LTRIM$(STR$(Shuffled(L0))); " ";
NEXT </lang>
Sample output:
before: 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 after: 37 5 4 12 29 25 34 20 40 23 31 1 14 6 18 15 50 38 45 0 30 28 24 26 21 11 16 41 2 42 48 35 36 49 7 22 32 44 33 43 9 13 8 51 17 39 27 47 3 10 46 19
C
This shuffles any "object"; it imitates qsort in the syntax.
<lang c>#include <stdlib.h>
- include <string.h>
inline int rrand(int m) {
return (int)((double)m * ( rand() / (RAND_MAX+1.0) ));
}
void shuffle(void *obj, size_t nmemb, size_t size) {
void *temp = malloc(size);
size_t n = nmemb;
while ( n > 1 ) {
size_t k = rrand(n--);
memcpy(temp, obj + n*size, size);
memcpy(obj + n*size, obj + k*size, size);
memcpy(obj + k*size, temp, size);
}
free(temp);
}</lang>
C++
Compiler: g++ (version 4.3.2 20081105 (Red Hat 4.3.2-7))
<lang cpp>#include <cstdlib>
- include <algorithm>
- include <iterator>
template<typename RandomAccessIterator> void knuthShuffle(RandomAccessIterator begin, RandomAccessIterator end) {
for(unsigned int n = end - begin - 1; n >= 1; --n) {
unsigned int k = rand() % (n + 1);
if(k != n) {
std::iter_swap(begin + k, begin + n);
}
}
}</lang>
C#
<lang csharp>public static void KnuthShuffle<T>(T[] array) {
System.Random random = new System.Random();
for (int i = 0; i < array.Length; i++)
{
int j = random.Next(array.Length);
T temp = array[i]; array[i] = array[j]; array[j] = temp;
}
}</lang>
Clojure
<lang lisp>(defn shuffle [vect]
(reduce (fn [v i] (let [r (rand-int i)]
(assoc v i (v r) r (v i)))
vect (range (dec (count vect)) 1 -1)))</lang>
This works by generating a sequence of end-indices from n-1 to 1, then reducing that sequence (starting with the original vector) through a function that, given a vector and end-index, performs a swap between the end-index and some random index less than the end-index.
Common Lisp
<lang lisp>(defun nshuffle (sequence)
(loop for i from (length sequence) downto 2
do (rotatef (elt sequence (random i))
(elt sequence (1- i))))
sequence)</lang>
This operates on arbitrary sequences, but will be inefficient applied to a list as opposed to a vector. Dispatching on type, and using an intermediate vector to hold the contents of list can make both cases more efficient (since the array specific case can use aref rather than elt):
<lang lisp>(defun nshuffle (sequence)
(etypecase sequence (list (nshuffle-list sequence)) (array (nshuffle-array sequence))))
(defun nshuffle-list (list)
"Shuffle the list using an intermediate vector." (let ((array (nshuffle-array (coerce list 'vector)))) (declare (dynamic-extent array)) (map-into list 'identity array)))
(defun nshuffle-array (array)
(loop for i from (length array) downto 2
do (rotatef (aref array (random i))
(aref array (1- i)))
finally (return array)))</lang>
E
<lang e>def shuffle(array, random) {
for bound in (2..(array.size())).descending() {
def i := random.nextInt(bound)
def swapTo := bound - 1
def t := array[swapTo]
array[swapTo] := array[i]
array[i] := t
}
}</lang>
<lang e>? def arr := [1,2,3,4,5,6,7,8,9,10].diverge()
- value: [1, 2, 3, 4, 5, 6, 7, 8, 9, 10].diverge()
? shuffle(arr, entropy) ? arr
- value: [4, 5, 2, 9, 7, 8, 1, 3, 6, 10].diverge()</lang>
Factor
There is a randomize word already in the standard library. Implementation:
<lang factor>: randomize ( seq -- seq )
dup length [ dup 1 > ] [ [ iota random ] [ 1 - ] bi [ pick exchange ] keep ] while drop ;</lang>
Forth
<lang forth>include random.fs
- shuffle ( deck size -- )
2 swap do dup i random cells + over @ over @ swap rot ! over ! cell+ -1 +loop drop ;
- .array 0 do dup @ . cell+ loop drop ;
create deck 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 ,
deck 10 2dup shuffle .array</lang>
Fortran
<lang fortran>program Knuth_Shuffle
implicit none
integer, parameter :: reps = 1000000 integer :: i, n integer, dimension(10) :: a, bins = 0, initial = (/ (n, n=1,10) /)
do i = 1, reps a = initial call Shuffle(a) where (a == initial) bins = bins + 1 ! skew tester end do write(*, "(10(i8))") bins
! prints 100382 100007 99783 100231 100507 99921 99941 100270 100290 100442
contains
subroutine Shuffle(a)
integer, intent(inout) :: a(:) integer :: i, randpos, temp real :: r
do i = size(a), 2, -1
call random_number(r)
randpos = int(r * i) + 1
temp = a(randpos)
a(randpos) = a(i)
a(i) = temp
end do
end subroutine Shuffle
end program Knuth_Shuffle</lang>
F#
Allows a shuffle of arrays of arbitrary items. Requires 2010 beta of F#. Lazily returns a sequence.
This is the original Fisher-Yates shuffle as described by the link: <lang fsharp>open System open System let FisherYatesShuffle (initialList : array<'a>) =
let availableFlags = Array.init initialList.Length (fun i -> (i, true))
// Which items are available and their indices
let rnd = new Random()
let nextItem nLeft =
let nItem = rnd.Next(0, nLeft) // Index out of available items
let index = // Index in original deck
availableFlags // Go through available array
|> Seq.filter (fun (ndx,f) -> f) // and pick out only the available tuples
|> Seq.nth nItem // Get the one at our chosen index
|> fst // and retrieve it's index into the original array
availableFlags.[index] <- (index, false) // Mark that index as unavailable
initialList.[index] // and return the original item
seq {(initialList.Length) .. -1 .. 1} // Going from the length of the list down to 1
|> Seq.map (fun i -> nextItem i) // yield the next item
</lang> Here's the modified Knuth shuffle which shuffles the original array in place <lang fsharp>let KnuthShuffle (lst : array<'a>) =
let Swap i j = // Standard swap
let item = lst.[i]
lst.[i] <- lst.[j]
lst.[j] <- item
let rnd = new Random()
let ln = lst.Length
[0..(ln - 2)] // For all indices except the last
|> Seq.iter (fun i -> Swap i (rnd.Next(i, ln))) // swap th item at the index with a random one following it (or itself)
lst // Return the list shuffled in place</lang>
Example: <lang fsharp>> KnuthShuffle [| "Darrell"; "Marvin"; "Doug"; "Greg"; "Sam"; "Ken" |];; val it : string array = [|"Marvin"; "Doug"; "Sam"; "Darrell"; "Ken"; "Greg"|] </lang>
Haskell
<lang Haskell>import System.Random import Data.List import Control.Monad import Control.Arrow
mkRands = mapM (randomRIO.(,)0 ). enumFromTo 1. pred
replaceAt :: Int -> a -> [a] -> [a] replaceAt i c = uncurry((.((c:).drop 1)).(++)). splitAt i
swapElems :: (Int, Int) -> [a] -> [a] swapElems (i,j) xs | i==j = xs
| otherwise = replaceAt j (xs!!i) $ replaceAt i (xs!!j) xs
knuthShuffle :: [a] -> IO [a] knuthShuffle xs =
liftM (foldr swapElems xs. zip [1..]) (mkRands (length xs))</lang>
Examples of use:
*Main> knuthShuffle ['a'..'k'] "bhjdgfciake" *Main> knuthShuffle $ map(ap (,)(+10)) [0..9] [(0,10),(8,18),(2,12),(3,13),(9,19),(4,14),(7,17),(1,11),(6,16),(5,15)]
Function for showing intermediate results: <lang Haskell>knuthShuffleProcess :: (Show a) => [a] -> IO () knuthShuffleProcess =
(mapM_ print. reverse =<<). ap (fmap. (. zip [1..]). scanr swapElems) (mkRands. length)</lang>
Detailed output example:
*Main> knuthShuffleProcess ['a'..'k'] "abcdefghijk" "abckefghijd" "jbckefghiad" "jbckeighfad" "jbckeihgfad" "jbhkeicgfad" "jbhiekcgfad" "jbeihkcgfad" "ibejhkcgfad" "iebjhkcgfad" "iebjhkcgfad"
An imperative implementation using arrays and the ST monad:
<lang haskell>import Data.Array.ST import Data.STRef import Control.Monad import Control.Monad.ST import Control.Arrow import System.Random
shuffle :: RandomGen g => [a] -> g -> ([a], g) shuffle list g = runST $ do
r <- newSTRef g
let rand range = liftM (randomR range) (readSTRef r) >>=
runKleisli (second (Kleisli $ writeSTRef r) >>> arr fst)
a <- newAry (1, len) list
forM_ [len, len - 1 .. 2] $ \n -> do
k <- rand (1, n)
liftM2 (,) (readArray a k) (readArray a n) >>=
runKleisli (Kleisli (writeArray a n) *** Kleisli (writeArray a k))
liftM2 (,) (getElems a) (readSTRef r)
where len = length list
newAry :: (Int, Int) -> [a] -> ST s (STArray s Int a)
newAry = newListArray</lang>
J
<lang j>KS=:{~ (2&{.@[ {`(|.@[)`]} >@])/@(,~(,.?@>:))@i.@#</lang> The input array is transformed to a rectangular array of indexes. By doing this all kinds of arrays can serve as input (see examples below). The process is imitated by using using a fold, swapping elements in a restricted part of this index-array in each fold step. <lang j>proces J
fold swap transform array <==> f / g y</lang>
Example of a transformed input: <lang j>(,~(,.?@>:))@i.@# 1+i.6 0 0 0 0 0 0 1 1 0 0 0 0 2 0 0 0 0 0 3 2 0 0 0 0 4 3 0 0 0 0 5 0 0 0 0 0 0 1 2 3 4 5</lang> The last row is the index-array that has to be shuffled. The other rows have valid indexes in the first two columns. The second column has a randomized value <= value first column.
The index-swapping is done by the part: <lang j>2&{.@[ {`(|.@[)`]} >@]</lang> Finally, the shuffled indexes select elements from the original array. <lang j>input { ~ shuffled indexes</lang> Examples:<lang j>]A=: 5+i.9 5 6 7 8 9 10 11 12 13</lang> Shuffle: <lang j>KS A 13 10 7 5 11 9 8 6 12</lang>Input <lang j>]M=: /:~(1 2 3,:2 3 4),(11 2 3,: 0 11 2),(1 1 1,:1 0),:1 1 1,:1 0 1
1 1 1 1 0 0
1 1 1 1 0 1
1 2 3 2 3 4
11 2 3
0 11 2</lang>Shuffle
<lang j>KS M 11 2 3
0 11 2
1 1 1 1 0 1
1 1 1 1 0 0
1 2 3 2 3 4</lang>Input
<lang j>]L=:'aA';'bbB';'cC%$';'dD@' +--+---+----+---+ |aA|bbB|cC%$|dD@| +--+---+----+---+</lang>Shuffle <lang j>KS L +--+----+---+---+ |aA|cC%$|dD@|bbB| +--+----+---+---+</lang> In J the shuffling of an arbitrary array can easily be implemented by the phrase ( ref http://www.jsoftware.com/jwiki/JPhrases/RandomNumbers ): <lang j>({~?~@#)</lang> Applied on the former examples: <lang j>({~?~@#) A 8 7 13 6 10 11 5 9 12
({~?~@#) M
1 1 1
1 0 1
1 2 3 2 3 4
11 2 3
0 11 2
1 1 1 1 0 0
({~?~@#) L
+----+---+--+---+ |cC%$|bbB|aA|dD@| +----+---+--+---+</lang>
Java
<lang java>import java.util.Random;
public static final Random gen = new Random();
// version for array of ints public static void shuffle (int[] array) {
int n = array.length;
while (n > 1) {
int k = gen.nextInt(n--); //decrements after using the value
int temp = array[n];
array[n] = array[k];
array[k] = temp;
}
} // version for array of references public static void shuffle (Object[] array) {
int n = array.length;
while (n > 1) {
int k = gen.nextInt(n--); //decrements after using the value
Object temp = array[n];
array[n] = array[k];
array[k] = temp;
}
}</lang>
JavaScript
<lang javascript>function knuth_shuffle(a) {
var n = a.length;
var r, temp;
while (n > 1) {
r = Math.floor(n * Math.random());
n--;
temp = a[n];
a[n] = a[r];
a[r] = temp;
}
return a;
}
var res = {'1,2,3': 0, '1,3,2': 0, '2,1,3': 0, '2,3,1': 0, '3,1,2': 0, '3,2,1': 0};
for (var i = 0; i < 100000; i++)
res[ knuth_shuffle([1,2,3]).join(',') ] ++;
for (var key in res)
print(key + "\t" + res[key]);</lang>
results in:
1,2,3 16619 1,3,2 16614 2,1,3 16752 2,3,1 16959 3,1,2 16460 3,2,1 16596
Logo
<lang logo>to swap :i :j :a
localmake "t item :i :a setitem :i :a item :j :a setitem :j :a :t
end to shuffle :a
for [i [count :a] 2] [swap 1 + random :i :i :a]
end
make "a {1 2 3 4 5 6 7 8 9 10} shuffle :a show :a</lang>
Lua
<lang lua>function table.shuffle(t)
local n = #t while n > 1 do local k = math.random(n) t[n], t[k] = t[k], t[n] n = n - 1 end return t
end math.randomseed( os.time() ) a = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10} table.shuffle(a) for i,v in ipairs(a) do print(i,v) end</lang>
M4
<lang M4>divert(-1) define(`randSeed',141592653) define(`rand_t',`eval(randSeed^(randSeed>>13))') define(`random',
`define(`randSeed',eval((rand_t^(rand_t<<18))&0x7fffffff))randSeed')
define(`for',
`ifelse($#,0,``$0, `ifelse(eval($2<=$3),1, `pushdef(`$1',$2)$4`'popdef(`$1')$0(`$1',incr($2),$3,`$4')')')')
define(`set',`define(`$1[$2]',`$3')') define(`get',`defn($1[$2])') define(`new',`set($1,size,0)') define(`deck',
`new($1)for(`x',1,$2,
`set(`$1',x,x)')`'set(`$1',size,$2)')
define(`show',
`for(`x',1,get($1,size),`get($1,x)`'ifelse(x,get($1,size),`',`, ')')')
define(`swap',`set($1,$2,get($1,$4))`'set($1,$4,$3)') define(`shuffle',
`define(`s',get($1,size))`'for(`x',1,decr(s),
`swap($1,x,get($1,x),eval(x+random%(s-x+1)))')')
divert
deck(`b',52) show(`b') shuffle(`b') show(`b')</lang>
Output:
1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52 6, 22, 33, 51, 35, 45, 16, 32, 7, 34, 10, 44, 5, 38, 43, 25, 29, 9, 37, 20, 21, 48, 24, 46, 8, 26, 41, 47, 49, 36, 14, 31, 15, 39, 12, 17, 13, 1, 3, 4, 27, 11, 28, 2, 19, 30, 42, 50, 18, 52, 40, 23
Mathematica
Usage of built-in function: <lang Mathematica>RandomSample[{1, 2, 3, 4, 5, 6}]</lang> Custom function: <lang Mathematica>Shuffle[input_List /; Length[input] >= 1] :=
Module[{indices = {}, allindices = Range[Length[input]]},
Do[
AppendTo[indices,
Complement[allindices, indices][[RandomInteger[{1, i}]]]];
,
{i, Length[input], 1, -1}
];
inputindices
]</lang>
Example: <lang Mathematica>Shuffle[{1, 2, 3, 4, 5, 6}]</lang>
Modula-3
<lang modula3>MODULE Shuffle EXPORTS Main;
IMPORT IO, Fmt, Random;
VAR a := ARRAY [0..9] OF INTEGER {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
PROCEDURE Shuffle(VAR a: ARRAY OF INTEGER) =
VAR temp: INTEGER;
n: INTEGER := NUMBER(a);
BEGIN
WITH rand = NEW(Random.Default).init() DO
WHILE n > 1 DO
WITH k = rand.integer(0, n - 1) DO
DEC(n);
temp := a[n];
a[n] := a[k];
a[k] := temp;
END;
END;
END;
END Shuffle;
BEGIN
Shuffle(a);
FOR i := FIRST(a) TO LAST(a) DO
IO.Put(Fmt.Int(a[i]) & " ");
END;
IO.Put("\n");
END Shuffle.</lang> Output:
martin@thinkpad:~$ ./shuffle 9 2 7 3 6 8 4 5 1 10 martin@thinkpad:~$ ./shuffle 1 7 8 10 5 4 6 3 9 2
OCaml
<lang ocaml>let shuffle arr =
for n = Array.length arr - 1 downto 1 do let k = Random.int (n + 1) in let temp = arr.(n) in arr.(n) <- arr.(k); arr.(k) <- temp done</lang>
Perl
<lang perl>sub shuffle
{my @a = @_;
foreach my $n (1 .. $#a)
{my $k = int rand $n + 1;
$k == $n or @a[$k, $n] = @a[$n, $k];}
return @a;}</lang>
Perl 6
<lang perl6>sub shuffle (@a is copy) {
for 1 ..^ @a -> $n {
my $k = (0 .. $n).pick;
$k == $n or @a[$k, $n] = @a[$n, $k];
}
return @a;
}</lang>
PowerShell
<lang powershell>function shuffle ($a) {
$c = $a.Clone() # make copy to avoid clobbering $a
1..($c.Length - 1) | ForEach-Object {
$i = Get-Random -Minimum $_ -Maximum $c.Length
$c[$_-1],$c[$i] = $c[$i],$c[$_-1]
$c[$_-1] # return newly-shuffled value
}
$c[-1] # last value
}</lang> This yields the values one by one instead of returning the array as a whole, so the rest of the pipeline can work on the values while shuffling is still in progress.
Python
Python's standard library function random.shuffle uses this algorithm. The function below is very similar:
<lang python>from random import randrange
def knuth_shuffle(x):
for i in reversed(range(1, len(x))):
j = randrange(i + 1)
x[i], x[j] = x[j], x[i]
x = list(range(10)) knuth_shuffle(x) print("shuffled:", x)</lang> Sample output
shuffled: [5, 1, 6, 0, 8, 4, 2, 3, 9, 7]
R
See also, the built-in function 'sample'.
Original Fisher-Yates version <lang r>fisheryatesshuffle <- function(n) {
pool <- seq_len(n)
a <- c()
while(length(pool) > 0)
{
k <- sample.int(length(pool), 1)
a <- c(a, pool[k])
pool <- pool[-k]
}
a
}</lang> Knuth variation: <lang r>fisheryatesknuthshuffle <- function(n) {
a <- seq_len(n)
while(n >=2)
{
k <- sample.int(n, 1)
if(k != n)
{
temp <- a[k]
a[k] <- a[n]
a[n] <- temp
}
n <- n - 1
}
a
}
- Example usage:
fisheryatesshuffle(6) # e.g. 1 3 6 2 4 5 x <- c("foo", "bar", "baz", "quux") x[fisheryatesknuthshuffle(4)] # e.g. "bar" "baz" "quux" "foo"</lang>
Ruby
<lang ruby>class Array
def knuth_shuffle!
j = length
i = 0
while j > 1
r = i + rand(j)
self[i], self[r] = self[r], self[i]
i += 1
j -= 1
end
self
end
end
r = Hash.new(0) 100_000.times do |i|
a = [1,2,3].knuth_shuffle! r[a] += 1
end
r.keys.sort.each {|a| puts "#{a.inspect} => #{r[a]}"}</lang> results in
[1, 2, 3] => 16572 [1, 3, 2] => 16610 [2, 1, 3] => 16633 [2, 3, 1] => 16714 [3, 1, 2] => 16838 [3, 2, 1] => 16633
Scheme
<lang scheme> (define (swap vec i j)
(let ([tmp (vector-ref vec i)]) (vector-set! vec i (vector-ref vec j)) (vector-set! vec j tmp)))
(define (shuffle vec)
(for ((i (in-range (- (vector-length vec) 1) 0 -1)))
(let ((r (random i)))
(swap vec i r)))
vec)
</lang>
> (shuffle (list->vector (for/list ((i (in-range 0 12))) i))) #(11 9 7 5 10 6 2 0 1 3 8 4)
Smalltalk
<lang smalltalk>"The selector swap:with: is documented, but it seems not
implemented (GNU Smalltalk version 3.0.4); so here it is an implementation"
SequenceableCollection extend [
swap: i with: j [ |t| t := self at: i. self at: i put: (self at: j). self at: j put: t. ]
].
Object subclass: Shuffler [
Shuffler class >> Knuth: aSequenceableCollection [
|n k|
n := aSequenceableCollection size.
[ n > 1 ] whileTrue: [
k := Random between: 1 and: n.
aSequenceableCollection swap: n with: k.
n := n - 1
]
]
].</lang>
Testing
<lang smalltalk>"Test" |c| c := OrderedCollection new. c addAll: #( 1 2 3 4 5 6 7 8 9 ). Shuffler Knuth: c. c display.</lang>
Tcl
<lang tcl>proc knuth_shuffle lst {
set j [llength $lst]
for {set i 0} {$j > 1} {incr i;incr j -1} {
set r [expr {$i+int(rand()*$j)}]
set t [lindex $lst $i]
lset lst $i [lindex $lst $r]
lset lst $r $t
}
return $lst
}
% knuth_shuffle {1 2 3 4 5} 2 1 3 5 4 % knuth_shuffle {1 2 3 4 5} 5 2 1 4 3 % knuth_shuffle {tom dick harry peter paul mary} tom paul mary harry peter dick</lang> As a test of skewing (an indicator of a poor implementation) this code was used: <lang tcl>% for {set i 0} {$i<100000} {incr i} {
foreach val [knuth_shuffle {1 2 3 4 5}] pos {pos0 pos1 pos2 pos3 pos4} {
incr tots($pos) $val
}
} % parray tots tots(pos0) = 300006 tots(pos1) = 300223 tots(pos2) = 299701 tots(pos3) = 299830 tots(pos4) = 300240</lang>
Ursala
This function works on lists of any type and length, including character strings.
<lang Ursala>shuffle = @iNX ~&l->r ^jrX/~&l ~&lK8PrC</lang>
test program: <lang Ursala>#cast %s
example = shuffle 'abcdefghijkl'</lang> output:
'keacfjlbdigh'
Vedit macro language
The shuffle routine in Playing Cards shuffles text lines in edit buffer. This example shuffles numeric registers #0 to #19.
The output will be inserted in current edit buffer.
<lang vedit>// Test main
- 90 = Time_Tick // seed for random number generator
- 99 = 20 // number of items in the array
IT("Before:") IN for (#100 = 0; #100 < #99; #100++) {
#@100 = #100
Num_Ins(#@100, LEFT+NOCR) IT(" ")
} IN
Call("SHUFFLE_NUMBERS")
IT("After:") IN for (#100 = 0; #100 < #99; #100++) {
Num_Ins(#@100, LEFT+NOCR) IT(" ")
} IN Return
//-------------------------------------------------------------- // Shuffle numeric registers #0 to #nn // #99 = number of registers to shuffle (nn-1) //
- SHUFFLE_NUMBERS:
for (#91 = #99-1; #91 > 0; #91--) {
Call("RANDOM")
#101 = Return_Value
#102 = #@101; #@101 = #@91; #@91 = #102
} Return
//-------------------------------------------------------------- // Generate random numbers in range 0 <= Return_Value < #91 // #90 = Seed (0 to 0x7fffffff) // #91 = Scaling (0 to 0x10000) //
- RANDOM:
- 92 = 0x7fffffff / 48271
- 93 = 0x7fffffff % 48271
- 90 = (48271 * (#90 % #92) - #93 * (#90 / #92)) & 0x7fffffff
Return ((#90 & 0xffff) * #91 / 0x10000)</lang>
Output:
Before: 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 After: 9 13 8 18 10 1 17 15 0 16 14 19 3 2 7 11 6 4 5 12