Sorting algorithms/Strand sort

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Task
Sorting algorithms/Strand sort
You are encouraged to solve this task according to the task description, using any language you may know.

Sorting Algorithm
This is a sorting algorithm. It may be applied to a set of data in order to sort it.

For other sorting algorithms, see Category:Sorting Algorithms, or:
O(n logn) Sorts
Heapsort | Mergesort | Quicksort
O(n log2n) Sorts
Shell Sort
O(n2) Sorts
Bubble sort | Cocktail sort | Comb sort | Gnome sort | Insertion sort | Selection sort | Strand sort
Other Sorts
Bead sort | Bogosort | Counting sort | Pancake sort | Permutation sort | Radix sort | Sleep sort | Stooge sort
This page uses content from Wikipedia. The original article was at Strand sort. The list of authors can be seen in the page history. As with Rosetta Code, the text of Wikipedia is available under the GNU FDL. (See links for details on variance)

Implement the Strand sort. This is a way of sorting numbers by extracting shorter sequences of already sorted numbers from an unsorted list.

Contents

[edit] AutoHotkey

Works with: AutoHotkey_L
string =
(
-2 0 -2 5 5 3 -1 -3 5 5 0 2 -4 4 2
)
string2 := string
Loop
{
loop, parse, string, %A_space%
{
list := 1 = A_index ? A_loopfield : list
StringSplit, k, list, %A_space%
 
if ( k%k0% <= A_loopfield ) && ( l != "" ) && ( A_index != 1 )
list := list . " " . A_loopfield
 
if ( k%k0% > A_loopfield )
list := A_loopfield . " " . list , index++
l := A_loopfield
}
if ( index = 0 )
{
MsgBox % "unsorted:" string2 "`n Sorted:" list
exitapp
}
string := list, list = "", index := 0
}
esc::ExitApp
outout
 
unsorted:-2 0 -2 5 5 3 -1 -3 5 5 0 2 -4 4 2
Sorted:-4 -3 -2 -2 -1 0 0 2 2 3 4 5 5 5 5

[edit] C

Strand sort using singly linked list. C99, compiled with gcc -std=c99

#include <stdio.h>
 
typedef struct node_t *node, node_t;
struct node_t { int v; node next; };
typedef struct { node head, tail; } slist;
 
void push(slist *l, node e) {
if (!l->head) l->head = e;
if (l->tail) l->tail->next = e;
l->tail = e;
}
 
node removehead(slist *l) {
node e = l->head;
if (e) {
l->head = e->next;
e->next = 0;
}
return e;
}
 
void join(slist *a, slist *b) {
push(a, b->head);
a->tail = b->tail;
}
 
void merge(slist *a, slist *b) {
slist r = {0};
while (a->head && b->head)
push(&r, removehead(a->head->v <= b->head->v ? a : b));
 
join(&r, a->head ? a : b);
*a = r;
b->head = b->tail = 0;
}
 
void sort(int *ar, int len)
{
node_t all[len];
 
// array to list
for (int i = 0; i < len; i++)
all[i].v = ar[i], all[i].next = i < len - 1 ? all + i + 1 : 0;
 
slist list = {all, all + len - 1}, rem, strand = {0}, res = {0};
 
for (node e = 0; list.head; list = rem) {
rem.head = rem.tail = 0;
while ((e = removehead(&list)))
push((!strand.head || e->v >= strand.tail->v) ? &strand : &rem, e);
 
merge(&res, &strand);
}
 
// list to array
for (int i = 0; res.head; i++, res.head = res.head->next)
ar[i] = res.head->v;
}
 
void show(const char *title, int *x, int len)
{
printf("%s ", title);
for (int i = 0; i < len; i++)
printf("%3d ", x[i]);
putchar('\n');
}
 
int main(void)
{
int x[] = {-2,0,-2,5,5,3,-1,-3,5,5,0,2,-4,4,2};
# define SIZE sizeof(x)/sizeof(int)
 
show("before sort:", x, SIZE);
sort(x, sizeof(x)/sizeof(int));
show("after sort: ", x, SIZE);
 
return 0;
}
outout
before sort:  -2   0  -2   5   5   3  -1  -3   5   5   0   2  -4   4   2
after sort: -4 -3 -2 -2 -1 0 0 2 2 3 4 5 5 5 5

[edit] C++

#include <list>
 
template <typename T>
std::list<T> strandSort(std::list<T> lst) {
if (lst.size() <= 1)
return lst;
std::list<T> result;
std::list<T> sorted;
while (!lst.empty()) {
sorted.push_back(lst.front());
lst.pop_front();
for (typename std::list<T>::iterator it = lst.begin(); it != lst.end(); ) {
if (sorted.back() <= *it) {
sorted.push_back(*it);
it = lst.erase(it);
} else
it++;
}
result.merge(sorted);
}
return result;
}

[edit] Clojure

(ns rosettacode.strand-sort)
 
(defn merge-join
"Produces a globally sorted seq from two sorted seqables"
[[a & la :as all] [b & lb :as bll]]
(cond (nil? a) bll
(nil? b) all
(< a b) (cons a (lazy-seq (merge-join la bll)))
true (cons b (lazy-seq (merge-join all lb)))))
 
(defn unbraid
"Separates a sorted list from a sequence"
[u]
(when (seq u)
(loop [[x & xs] u
u []
s []
e x]
(if (nil? x)
[s u]
(if (>= x e)
(recur xs u (conj s x) x)
(recur xs (conj u x) s e))))))
 
(defn strand-sort
"http://en.wikipedia.org/wiki/Strand_sort"
[s]
(loop [[s u] (unbraid s)
m nil]
(if s
(recur (unbraid u) (merge-join m s))
m)))
 
(strand-sort [1, 6, 3, 2, 1, 7, 5, 3])
;;=> (1 1 2 3 3 5 6 7)
 

[edit] CMake

Only for lists of integers.

# strand_sort(<output variable> [<value>...]) sorts a list of integers.
function(strand_sort var)
# Strand sort moves elements from _ARGN_ to _answer_.
set(answer) # answer: a sorted list
while(DEFINED ARGN)
# Split _ARGN_ into two lists, _accept_ and _reject_.
set(accept) # accept: elements in sorted order
set(reject) # reject: all other elements
set(p)
foreach(e ${ARGN})
if(DEFINED p AND p GREATER ${e})
list(APPEND reject ${e})
else()
list(APPEND accept ${e})
set(p ${e})
endif()
endforeach(e)
 
# Prepare to merge _accept_ into _answer_. First, convert both lists
# into arrays, for better indexing: set(e ${answer${i}}) is faster
# than list(GET answer ${i} e).
set(la 0)
foreach(e ${answer})
math(EXPR la "${la} + 1")
set(answer${la} ${e})
endforeach(e)
set(lb 0)
foreach(e ${accept})
math(EXPR lb "${lb} + 1")
set(accept${lb} ${e})
endforeach(e)
 
# Merge _accept_ into _answer_.
set(answer)
set(ia 1)
set(ib 1)
while(NOT ia GREATER ${la}) # Iterate elements of _answer_.
set(ea ${answer${ia}})
while(NOT ib GREATER ${lb}) # Take elements from _accept_,
set(eb ${accept${ib}}) # while they are less than
if(eb LESS ${ea}) # next element of _answer_.
list(APPEND answer ${eb})
math(EXPR ib "${ib} + 1")
else()
break()
endif()
endwhile()
list(APPEND answer ${ea}) # Take next from _answer_.
math(EXPR ia "${ia} + 1")
endwhile()
while(NOT ib GREATER ${lb}) # Take rest of _accept_.
list(APPEND answer ${accept${ib}})
math(EXPR ib "${ib} + 1")
endwhile()
 
# This _reject_ becomes next _ARGN_. If _reject_ is empty, then
# set(ARGN) undefines _ARGN_, breaking the loop.
set(ARGN ${reject})
endwhile(DEFINED ARGN)
 
set("${var}" ${answer} PARENT_SCOPE)
endfunction(strand_sort)
strand_sort(result 11 55 55 44 11 33 33 44 22 22)
message(STATUS "${result}") # -- 11;11;22;22;33;33;44;44;55;55

[edit] Common Lisp

(defun strand-sort (l cmp)
(if l
(let* ((l (reverse l))
(o (list (car l))) n)
(loop for i in (cdr l) do
(push i (if (funcall cmp (car o) i) n o)))
(merge 'list o (strand-sort n cmp) #'<))))
 
(let ((r (loop repeat 15 collect (random 10))))
(print r)
(print (strand-sort r #'<)))
output
(5 8 6 0 6 8 4 7 0 7 1 5 3 3 6) 
(0 0 1 3 3 4 5 5 6 6 6 7 7 8 8)

[edit] D

[edit] Using doubly linked lists

import std.stdio, std.container;
 
DList!T strandSort(T)(DList!T list) {
static DList!T merge(DList!T left, DList!T right) {
DList!T result;
while (!left.empty && !right.empty) {
if (left.front <= right.front) {
result.insertBack(left.front);
left.removeFront();
} else {
result.insertBack(right.front);
right.removeFront();
}
}
result.insertBack(left[]);
result.insertBack(right[]);
return result;
}
 
DList!T result, sorted, leftover;
 
while (!list.empty) {
leftover.clear();
sorted.clear();
sorted.insertBack(list.front);
list.removeFront();
foreach (item; list) {
if (sorted.back <= item)
sorted.insertBack(item);
else
leftover.insertBack(item);
}
result = merge(sorted, result);
list = leftover;
}
 
return result;
}
 
void main() {
auto lst = DList!int([-2,0,-2,5,5,3,-1,-3,5,5,0,2,-4,4,2]);
foreach (e; strandSort(lst))
write(e, " ");
}
Output:
-4 -3 -2 -2 -1 0 0 2 2 3 4 5 5 5 5 

[edit] Faster version using slices

import std.stdio, std.array;
 
T[] strandSort(T)(const(T)[] list) pure nothrow {
static T[] merge(const(T)[] left, const(T)[] right) pure nothrow {
T[] res;
while (!left.empty && !right.empty) {
if (left.front <= right.front) {
res ~= left.front;
left.popFront;
} else {
res ~= right.front;
right.popFront;
}
}
return res ~ left ~ right;
}
 
T[] result;
while (!list.empty) {
auto sorted = list[0 .. 1];
list.popFront;
typeof(sorted) leftover;
foreach (const item; list)
(sorted.back <= item ? sorted : leftover) ~= item;
result = merge(sorted, result);
list = leftover;
}
 
return result;
}
 
void main() {
const arr = [-2, 0, -2, 5, 5, 3, -1, -3, 5, 5, 0, 2, -4, 4, 2];
arr.strandSort.writeln;
}
Output:
[-4, -3, -2, -2, -1, 0, 0, 2, 2, 3, 4, 5, 5, 5, 5]

[edit] Euphoria

function merge(sequence left, sequence right)
sequence result
result = {}
while length(left) > 0 and length(right) > 0 do
if left[$] <= right[1] then
exit
elsif right[$] <= left[1] then
return result & right & left
elsif left[1] < right[1] then
result = append(result,left[1])
left = left[2..$]
else
result = append(result,right[1])
right = right[2..$]
end if
end while
return result & left & right
end function
 
function strand_sort(sequence s)
integer j
sequence result
result = {}
while length(s) > 0 do
j = length(s)
for i = 1 to length(s)-1 do
if s[i] > s[i+1] then
j = i
exit
end if
end for
 
result = merge(result,s[1..j])
s = s[j+1..$]
end while
return result
end function
 
constant s = rand(repeat(1000,10))
puts(1,"Before: ")
? s
puts(1,"After: ")
? strand_sort(s)

Output:

Before: {551,746,940,903,51,18,346,417,340,502}
After:  {18,51,340,346,417,502,551,746,903,940}

[edit] Go

package main
 
import "fmt"
 
type link struct {
int
next *link
}
 
func linkInts(s []int) *link {
if len(s) == 0 {
return nil
}
return &link{s[0], linkInts(s[1:])}
}
 
func (l *link) String() string {
if l == nil {
return "nil"
}
r := fmt.Sprintf("[%d", l.int)
for l = l.next; l != nil; l = l.next {
r = fmt.Sprintf("%s %d", r, l.int)
}
return r + "]"
}
 
func main() {
a := linkInts([]int{170, 45, 75, -90, -802, 24, 2, 66})
fmt.Println("before:", a)
b := strandSort(a)
fmt.Println("after: ", b)
}
 
func strandSort(a *link) (result *link) {
for a != nil {
// build sublist
sublist := a
a = a.next
sTail := sublist
for p, pPrev := a, a; p != nil; p = p.next {
if p.int > sTail.int {
// append to sublist
sTail.next = p
sTail = p
// remove from a
if p == a {
a = p.next
} else {
pPrev.next = p.next
}
} else {
pPrev = p
}
}
sTail.next = nil // terminate sublist
if result == nil {
result = sublist
continue
}
// merge
var m, rr *link
if sublist.int < result.int {
m = sublist
sublist = m.next
rr = result
} else {
m = result
rr = m.next
}
result = m
for {
if sublist == nil {
m.next = rr
break
}
if rr == nil {
m.next = sublist
break
}
if sublist.int < rr.int {
m.next = sublist
m = sublist
sublist = m.next
} else {
m.next = rr
m = rr
rr = m.next
}
}
}
return
}

Output:

before: [170 45 75 -90 -802 24 2 66]
after:  [-802 -90 2 24 45 66 75 170]

[edit] Haskell

-- Same merge as in Merge Sort
merge :: (Ord a) => [a] -> [a] -> [a]
merge [] ys = ys
merge xs [] = xs
merge (x : xs) (y : ys)
| x <= y = x : merge xs (y : ys)
| otherwise = y : merge (x : xs) ys
 
strandSort :: (Ord a) => [a] -> [a]
strandSort [] = []
strandSort (x : xs) = merge strand (strandSort rest) where
(strand, rest) = extractStrand x xs
extractStrand x [] = ([x], [])
extractStrand x (x1 : xs)
| x <= x1 = let (strand, rest) = extractStrand x1 xs in (x : strand, rest)
| otherwise = let (strand, rest) = extractStrand x xs in (strand, x1 : rest)

[edit] J

Generally, this task should be accomplished in J using /:~. Here we take an approach that's more comparable with the other examples on this page.

Using merge defined at Sorting algorithms/Merge sort#J:

strandSort=: (#~ merge $:^:(0<#)@(#~ -.)) (= >./\)

Example use:

   strandSort 3 1 5 4 2
1 2 3 4 5

Note: the order in which this J implementation processes the strands differs from the pseudocode currently at the wikipedia page on strand sort and matches the haskell implementation currently at the wikipedia page.

Also note that the individual strands can be seen by using ; instead of merge.

   ((#~ ; $:^:(0<#)@(#~ -.)) (= >./\)) 3 1 5 4 2
┌───┬───┬─┬┐
3 51 42││
└───┴───┴─┴┘
((#~ ; $:^:(0<#)@(#~ -.)) (= >./\)) 3 3 1 2 4 3 5 6
┌─────────┬─────┬┐
3 3 4 5 61 2 3││
└─────────┴─────┴┘

[edit] Java

Works with: Java version 1.6+
import java.util.Arrays;
import java.util.LinkedList;
 
public class Strand{
// note: the input list is destroyed
public static <E extends Comparable<? super E>>
LinkedList<E> strandSort(LinkedList<E> list){
if(list.size() <= 1) return list;
 
LinkedList<E> result = new LinkedList<E>();
while(list.size() > 0){
LinkedList<E> sorted = new LinkedList<E>();
sorted.add(list.removeFirst()); //same as remove() or remove(0)
for(Iterator<E> it = list.iterator(); it.hasNext(); ){
E elem = it.next();
if(sorted.peekLast().compareTo(elem) <= 0){
sorted.addLast(elem); //same as add(elem) or add(0, elem)
it.remove();
}
}
result = merge(sorted, result);
}
return result;
}
 
private static <E extends Comparable<? super E>>
LinkedList<E> merge(LinkedList<E> left, LinkedList<E> right){
LinkedList<E> result = new LinkedList<E>();
while(!left.isEmpty() && !right.isEmpty()){
//change the direction of this comparison to change the direction of the sort
if(left.peek().compareTo(right.peek()) <= 0)
result.add(left.remove());
else
result.add(right.remove());
}
result.addAll(left);
result.addAll(right);
return result;
}
 
public static void main(String[] args){
System.out.println(strandSort(new LinkedList<Integer>(Arrays.asList(3,1,2,4,5))));
System.out.println(strandSort(new LinkedList<Integer>(Arrays.asList(3,3,1,2,4,5))));
System.out.println(strandSort(new LinkedList<Integer>(Arrays.asList(3,3,1,2,4,3,5,6))));
}
}

Output:

[1, 2, 3, 4, 5]
[1, 2, 3, 3, 4, 5]
[1, 2, 3, 3, 3, 4, 5, 6]

[edit] jq

Most of the implementation is the "merge" function for merging two arrays. Notice that the helper function, strand, is defined here as an inner function.
# merge input array with array x by comparing the heads of the arrays 
# in turn; # if both arrays are sorted, the result will be sorted:
def merge(x):
length as $length
| (x|length) as $xl
| if $length == 0 then x
elif $xl == 0 then .
else
. as $in
| reduce range(0; $xl + $length) as $z
# state [ix, xix, ans]
( [0, 0, []];
if .[0] < $length and
((.[1] < $xl and $in[.[0]] <= x[.[1]]) or .[1] == $xl)
then [(.[0] + 1), .[1], (.[2] + [$in[.[0]]]) ]
else [.[0], (.[1] + 1), (.[2] + [x[.[1]]]) ]
end
) | .[2]
end ;
 
def strand_sort:
# The inner function emits [strand, remainder]
def strand:
if length <= 1 then .
else
reduce .[] as $x
# state: [strand, remainder]
([ [], [] ];
if ((.[0]|length) == 0) or .[0][-1] <= $x
then [ (.[0] + [$x]), .[1] ]
else [ .[0], (.[1] + [$x]) ]
end )
end ;
 
if length <= 1 then .
else strand as $s
| ($s[0] | merge( $s[1] | strand_sort))
end ;
 

Example:

[1,3,5,2,4,6] | strand_sort


[edit] Mathematica

StrandSort[ input_ ] := Module[ {results = {}, A = input},
While[Length@A > 0,
sublist = {A[[1]]}; A = A[[2;;All]];
For[i = 1, i < Length@A, i++,
If[ A[[i]] > Last@sublist, AppendTo[sublist, A[[i]]]; A = Delete[A, i];]
];
results = #[[Ordering@#]]&@Join[sublist, results];];
results ]

Example usage :

StrandSort[{2, 3, 7, 5, 1, 4, 7}]
{1, 2, 3, 4, 5, 7, 7}

[edit] MAXScript

fn strandSort arr =
(
arr = deepcopy arr
local sub = #()
local results = #()
while arr.count > 0 do
(
sub = #()
append sub (amax arr)
deleteitem arr (for i in 1 to arr.count where arr[i] == amax arr collect i)[1]
local i = 1
while i <= arr.count do
(
if arr[i] > sub[sub.count] do
(
append sub arr[i]
deleteitem arr i
)
i += 1
)
results = join sub results
)
return results
 
)

Output:

 
a = for i in 1 to 20 collect random 1 40
#(19, 26, 14, 31, 11, 33, 2, 14, 32, 28, 12, 38, 2, 37, 27, 18, 31, 24, 39, 28)
strandSort a
#(2, 2, 11, 12, 14, 14, 18, 19, 24, 26, 27, 28, 28, 31, 31, 32, 33, 37, 38, 39)
 

[edit] NetRexx

/* NetRexx */
options replace format comments java crossref savelog symbols binary
 
import java.util.List
 
placesList = [String -
"UK London", "US New York", "US Boston", "US Washington" -
, "UK Washington", "US Birmingham", "UK Birmingham", "UK Boston" -
]
 
lists = [ -
placesList -
, strandSort(String[] Arrays.copyOf(placesList, placesList.length)) -
]
 
loop ln = 0 to lists.length - 1
cl = lists[ln]
loop ct = 0 to cl.length - 1
say cl[ct]
end ct
say
end ln
 
return
 
method strandSort(A = String[]) public constant binary returns String[]
 
rl = String[A.length]
al = List strandSort(Arrays.asList(A))
al.toArray(rl)
 
return rl
 
method strandSort(Alst = List) public constant binary returns ArrayList
 
A = ArrayList(Alst)
result = ArrayList()
loop label A_ while A.size > 0
sublist = ArrayList()
sublist.add(A.get(0))
A.remove(0)
loop i_ = 0 while i_ < A.size - 1
if (Comparable A.get(i_)).compareTo(Comparable sublist.get(sublist.size - 1)) > 0 then do
sublist.add(A.get(i_))
A.remove(i_)
end
end i_
result = merge(result, sublist)
end A_
 
return result
 
method merge(left = List, right = List) public constant binary returns ArrayList
 
result = ArrayList()
loop label mx while left.size > 0 & right.size > 0
if (Comparable left.get(0)).compareTo(Comparable right.get(0)) <= 0 then do
result.add(left.get(0))
left.remove(0)
end
else do
result.add(right.get(0))
right.remove(0)
end
end mx
if left.size > 0 then do
result.addAll(left)
end
if right.size > 0 then do
result.addAll(right)
end
 
return result
 
Output
UK  London
US  New York
US  Boston
US  Washington
UK  Washington
US  Birmingham
UK  Birmingham
UK  Boston

UK  Birmingham
UK  Boston
UK  London
UK  Washington
US  Birmingham
US  Boston
US  New York
US  Washington

[edit] Nimrod

proc mergeList[T](a, b: var seq[T]): seq[T] =
result = @[]
while a.len > 0 and b.len > 0:
if a[0] < b[0]:
result.add a[0]
a.delete 0
else:
result.add b[0]
b.delete 0
result.add a
result.add b
 
proc strand[T](a: var seq[T]): seq[T] =
var i = 0
result = @[a[0]]
a.delete 0
while i < a.len:
if a[i] > result[result.high]:
result.add a[i]
a.delete i
else:
inc i
 
proc strandSort[T](a: seq[T]): seq[T] =
var a = a
result = a.strand
while a.len > 0:
var s = a.strand
result = mergeList(result, s)
 
var a = @[1, 6, 3, 2, 1, 7, 5, 3]
echo a.strandSort

Output:

@[1, 1, 2, 3, 3, 5, 6, 7]

[edit] OCaml

Translation of: Haskell
let rec strand_sort (cmp : 'a -> 'a -> int) : 'a list -> 'a list = function
[] -> []
| x::xs ->
let rec extract_strand x = function
[] -> [x], []
| x1::xs when cmp x x1 <= 0 ->
let strand, rest = extract_strand x1 xs in x::strand, rest
| x1::xs ->
let strand, rest = extract_strand x xs in strand, x1::rest
in
let strand, rest = extract_strand x xs in
List.merge cmp strand (strand_sort cmp rest)

usage

# strand_sort compare [170; 45; 75; -90; -802; 24; 2; 66];;
- : int list = [-802; -90; 2; 24; 45; 66; 75; 170]

[edit] PARI/GP

strandSort(v)={
my(sorted=[],unsorted=v,remaining,working);
while(#unsorted,
remaining=working=List();
listput(working, unsorted[1]);
for(i=2,#unsorted,
if(unsorted[i]<working[#working],
listput(remaining, unsorted[i])
,
listput(working, unsorted[i])
)
);
unsorted=Vec(remaining);
sorted=merge(sorted, Vec(working))
);
sorted
};
merge(u,v)={
my(ret=vector(#u+#v),i=1,j=1);
for(k=1,#ret,
if(i<=#u & (j>#v | u[i]<v[j]),
ret[k]=u[i];
i++
,
ret[k]=v[j];
j++
)
);
ret
};

[edit] Pascal

program StrandSortDemo;
 
type
TIntArray = array of integer;
 
function merge(left: TIntArray; right: TIntArray): TIntArray;
var
i, j, k: integer;
begin
setlength(merge, length(left) + length(right));
i := low(merge);
j := low(left);
k := low(right);
repeat
if ((left[j] <= right[k]) and (j <= high(left))) or (k > high(right)) then
begin
merge[i] := left[j];
inc(j);
end
else
begin
merge[i] := right[k];
inc(k);
end;
inc(i);
until i > high(merge);
end;
 
function StrandSort(s: TIntArray): TIntArray;
var
strand: TIntArray;
i, j: integer;
begin
setlength(StrandSort, length(s));
setlength(strand, length(s));
i := low(s);
repeat
StrandSort[i] := s[i];
inc(i);
until (s[i] < s[i-1]);
setlength(StrandSort, i);
repeat
setlength(strand, 1);
j := low(strand);
strand[j] := s[i];
while (s[i+1] > s[i]) and (i < high(s)) do
begin
inc(i);
inc(j);
setlength(strand, length(strand) + 1);
Strand[j] := s[i];
end;
StrandSort := merge(StrandSort, strand);
inc(i);
until (i > high(s));
end;
 
var
data: TIntArray;
i: integer;
 
begin
setlength(data, 8);
Randomize;
writeln('The data before sorting:');
for i := low(data) to high(data) do
begin
data[i] := Random(high(data));
write(data[i]:4);
end;
writeln;
data := StrandSort(data);
writeln('The data after sorting:');
for i := low(data) to high(data) do
begin
write(data[i]:4);
end;
writeln;
end.

[edit] Perl

use 5.10.0;    # for given/when
sub merge {
my ($x, $y) = @_;
my @out;
while (@$x and @$y) {
given ($x->[-1] <=> $y->[-1]) {
when( 1) { unshift @out, pop @$x }
when(-1) { unshift @out, pop @$y }
default { splice @out, 0, 0, pop(@$x), pop(@$y) }
}
}
return @$x, @$y, @out
}
 
sub strand {
my $x = shift;
my @out = shift @$x // return;
if (@$x) {
for (-@$x .. -1) {
if ($x->[$_] >= $out[-1]) {
push @out, splice @$x, $_, 1
}
}
}
return @out
}
 
sub strand_sort {
my @x = @_;
my @out;
while (my @strand = strand(\@x)) {
@out = merge(\@out, \@strand)
}
@out
}
 
my @a = map (int rand(100), 1 .. 10);
say "Before @a";
@a = strand_sort(@a);
say "After @a";

[edit] Perl 6

sub infix:<M> (@x, @y) {
gather {
while @x and @y {
take do given @x[0] cmp @y[0] {
when Increase { @x.shift }
when Decrease { @y.shift }
when Same { @x.shift, @y.shift }
}
}
take @x, @y;
}
}
 
sub strand (@x is rw) {
my $prev = -Inf;
my $i = 0;
gather while $i < @x {
if @x[$i] before $prev {
$i++;
}
else {
take $prev = splice(@x, $i, 1)[0];
}
}
}
 
sub strand_sort (@x is copy) {
my @out;
@out M= strand(@x) while @x;
@out;
}
 
my @a = (^100).roll(10);
say "Before @a[]";
@a = strand_sort(@a);
say "After @a[]";
 
@a = <The quick brown fox jumps over the lazy dog>;
say "Before @a[]";
@a = strand_sort(@a);
say "After @a[]";
Output:
Before 1 20 64 72 48 75 96 55 42 74
After  1 20 42 48 55 64 72 74 75 96
Before The quick brown fox jumps over the lazy dog
After  The brown dog fox jumps lazy over quick the

[edit] PHP

Translation of: D
Works with: PHP 5.3.0+
$lst = new SplDoublyLinkedList();
foreach (array(1,20,64,72,48,75,96,55,42,74) as $v)
$lst->push($v);
foreach (strandSort($lst) as $v)
echo "$v ";
 
function strandSort(SplDoublyLinkedList $lst) {
$result = new SplDoublyLinkedList();
while (!$lst->isEmpty()) {
$sorted = new SplDoublyLinkedList();
$remain = new SplDoublyLinkedList();
$sorted->push($lst->shift());
foreach ($lst as $item) {
if ($sorted->top() <= $item) {
$sorted->push($item);
} else {
$remain->push($item);
}
}
$result = _merge($sorted, $result);
$lst = $remain;
}
return $result;
}
 
function _merge(SplDoublyLinkedList $left, SplDoublyLinkedList $right) {
$res = new SplDoublyLinkedList();
while (!$left->isEmpty() && !$right->isEmpty()) {
if ($left->bottom() <= $right->bottom()) {
$res->push($left->shift());
} else {
$res->push($right->shift());
}
}
foreach ($left as $v) $res->push($v);
foreach ($right as $v) $res->push($v);
return $res;
}
1 20 42 48 55 64 72 74 75 96

[edit] PicoLisp

(de strandSort (Lst)
(let Res NIL # Result list
(while Lst
(let Sub (circ (car Lst)) # Build sublist as fifo
(setq
Lst (filter
'((X)
(or
(> (car Sub) X)
(nil (fifo 'Sub X)) ) )
(cdr Lst) )
Res (make
(while (or Res Sub) # Merge
(link
(if2 Res Sub
(if (>= (car Res) (cadr Sub))
(fifo 'Sub)
(pop 'Res) )
(pop 'Res)
(fifo 'Sub) ) ) ) ) ) ) )
Res ) )

Test:

: (strandSort (3 1 5 4 2))
-> (1 2 3 4 5)

: (strandSort (3 abc 1 (d e f) 5 T 4 NIL 2))
-> (NIL 1 2 3 4 5 abc (d e f) T)

[edit] PL/I

strand: procedure options (main); /* 27 Oct. 2012 */
declare A(100) fixed, used(100) bit (1), sorted fixed controlled;
declare (temp, work) fixed controlled;
declare (i, j, k, n) fixed binary;
 
n = hbound(A, 1);
used = '1'b;
A = random()*99;
 
put edit (A) (f(3));
 
do while (allocation(sorted) < n);
call fetch (A, work);
call move (temp, work);
 
call merge(sorted, temp);
/* Merges elements in SORTED with elements in TEMP. */
end;
/* Transfer the sorted elements to A. */
do i = 1 to allocation(sorted);
A(i) = sorted; free sorted;
end;
/* Print the sorted values. */
put skip list ('The sorted values are:');
put skip edit (A) (f(3));
 
/* Merges elements of SORTED with elements of TEMP and places */
/* the result in SORTED. */
/* Elements in SORTED and TEMP are in forward order. */
merge: procedure (sorted, temp);
declare (sorted, temp) fixed controlled;
declare work fixed controlled;
declare (j_ok, k_ok) bit (1);
 
do until ((k_ok | j_ok) = '0'b);
k_ok = allocation(sorted) > 0;
j_ok = allocation(temp) > 0;
if k_ok & j_ok then
do;
if sorted <= temp then
do; allocate work; work = sorted; free sorted; end;
else
do; allocate work; work = temp; free temp; end;
end;
else
if allocation(temp) = 0 then
/* temp is empty; copy remainder of sorted into work */
do while (allocation(sorted) > 0);
allocate work; work = sorted; free sorted;
end;
else
/* sorted is empty; copy remainder of temp onto work */
do while (allocation(temp) > 0);
allocate work; work = temp; free temp;
end;
end;
 
call move (sorted, work); /* Move the values to SORTED. */
 
end merge;
 
/* Collect a thread of ascending values from aray A, and stack them in temp. */
/* Note: the values in temp are in reverse order. */
fetch: procedure (A, temp);
declare A(*) fixed, temp controlled fixed;
declare i fixed binary;
 
do i = 1 to hbound(A,1);
if used(i) then
do; allocate temp; temp = A(i); used(i) = '0'b; go to found; end;
end;
found:
do i = i+1 to hbound(A,1);
if (temp <= A(i)) & used(i) then
do; allocate temp; temp = A(i); used(i) = '0'b; end;
end;
end fetch;
 
/* Copy the stack at TEMP to the stack at SORTED. */
/* In TEMP, elements are in reverse order; */
/* in SORTED, elements are in forward order. */
move: procedure (sorted, temp);
declare (sorted, temp) fixed controlled;
 
do while (allocation(sorted) > 0); free sorted; end;
do while (allocation (temp) > 0);
allocate sorted; sorted = temp; free temp;
end;
end move;
 
end strand;

Generated data:

 43  5 79 16 90 48 29 73 29 19 77 59 49  2 54 35 39 71 25 76 34 48 31 91 28 13 23 70 27 59 96  7 63 82 59 81 28 96 34 43
 81 98 21 47 72 57 45 64 94 51 18 11 65 12 61 97 13 84 95 89 43  8 14 31 58 68 58 39 59 26 72 38 26 85 30 89 42 90 29 11
 14 63 97 60  1 17 45 42 62 29 45 15 69 11 29 25 11 48 92  3

Results:

The sorted values are: 
  1  2  3  5  7  8 11 11 11 11 12 13 13 14 14 15 16 17 18 19 21 23 25 25 26 26 27 28 28 29 29 29 29 29 30 31 31 34 34 35
 38 39 39 42 42 43 43 43 45 45 45 47 48 48 48 49 51 54 57 58 58 59 59 59 59 60 61 62 63 63 64 65 68 69 70 71 72 72 73 76
 77 79 81 81 82 84 85 89 89 90 90 91 92 94 95 96 96 97 97 98

[edit] PureBasic

Procedure strandSort(List a())
Protected NewList subList()
Protected NewList results()
 
While ListSize(a()) > 0
ClearList(subList())
AddElement(subList())
FirstElement(a())
subList() = a()
DeleteElement(a())
ForEach a()
If a() >= subList()
AddElement(subList())
subList() = a()
DeleteElement(a())
EndIf
Next
 
;merge lists
FirstElement(subList())
If Not FirstElement(results())
;copy all of sublist() to results()
MergeLists(subList(), results(), #PB_List_Last)
Else
Repeat
If subList() < results()
InsertElement(results())
results() = subList()
DeleteElement(subList())
If Not NextElement(subList())
Break
EndIf
ElseIf Not NextElement(results())
;add remainder of sublist() to end of results()
MergeLists(subList(), results(), #PB_List_Last)
Break
EndIf
ForEver
EndIf
 
Wend
CopyList(results(), a())
EndProcedure
 
Procedure.s listContents(List a())
Protected output.s
PushListPosition(a())
ForEach a()
output + Str(a()) + ","
Next
PopListPosition(a())
ProcedureReturn Left(output, Len(output) - 1)
EndProcedure
 
Procedure setupList(List a())
ClearList(a())
Protected elementCount, i
 
elementCount = Random(5) + 10
For i = 1 To elementCount
AddElement(a())
a() = Random(10) - 5
Next
EndProcedure
 
 
If OpenConsole()
NewList sample()
Define i
 
For i = 1 To 3
setupList(sample())
PrintN("List " + Str(i) + ":")
PrintN(" Before: " + listContents(sample()))
strandSort(sample())
PrintN(" After : " + listContents(sample()))
PrintN("")
Next
 
Print(#CRLF$ + #CRLF$ + "Press ENTER to exit"): Input()
CloseConsole()
EndIf

Sample output:

List 1:
  Before:  3,-2,-4,4,-1,-3,-2,-2,2,2,0
  After :  -4,-3,-2,-2,-2,-1,0,2,2,3,4

List 2:
  Before:  -4,4,3,-2,3,-2,5,0,-1,0,5,1
  After :  -4,-2,-2,-1,0,0,1,3,3,4,5,5

List 3:
  Before:  -2,0,-2,5,5,3,-1,-3,5,5,0,2,-4,4,2
  After :  -4,-3,-2,-2,-1,0,0,2,2,3,4,5,5,5,5

[edit] Python

def merge_list(a, b):
out = []
while len(a) and len(b):
if a[0] < b[0]:
out.append(a.pop(0))
else:
out.append(b.pop(0))
out += a
out += b
return out
 
def strand(a):
i, s = 0, [a.pop(0)]
while i < len(a):
if a[i] > s[-1]:
s.append(a.pop(i))
else:
i += 1
return s
 
def strand_sort(a):
out = strand(a)
while len(a):
out = merge_list(out, strand(a))
return out
 
print strand_sort([1, 6, 3, 2, 1, 7, 5, 3])
Output:
[1, 1, 2, 3, 3, 5, 6, 7]

[edit] Racket

 
#lang racket
(require mzlib/list)
(define (merge xs ys) (merge-sorted-lists xs ys <=))
 
(define (strand-sort xs)
(let loop ([xs xs] [ys '[]])
(cond [(empty? xs) ys]
[else (define-values (sorted unsorted) (extract-strand xs))
(loop unsorted (merge sorted ys))])))
 
(define (extract-strand xs)
(for/fold ([strand '()] [unsorted '[]]) ([x xs])
(if (or (empty? strand) (< x (first strand)))
(values (cons x strand) unsorted)
(values strand (cons x unsorted)))))
 
(strand-sort (build-list 10 (λ(_) (random 15))))
 

[edit] REXX

This REXX program was written to generate a specified amount of random numbers as well as allowing a pre-pended list of numbers).
It can handle integers, floating point numbers, exponentated numbers, and character strings.

/*REXX pgm sorts a random list of words using the strand sort algorithm.*/
parse arg size minv maxv,old /*get options from command line. */
if size=='' then size=20 /*no size? Then use the default.*/
if minv=='' then minv=0 /*no minV? " " " " */
if maxv=='' then maxv=size /*no maxV? " " " " */
do i=1 for size /*generate random # list*/
old=old random(0,maxv-minv)+minv
end /*i*/
old=space(old) /*remove any extraneous blanks. */
say center('unsorted list',length(old),"─"); say old; say
new=strand_sort(old) /*sort the list of random numbers*/
say center('sorted list' ,length(new),"─"); say new
exit /*stick a fork in it, we're done.*/
/*──────────────────────────────────STRAND_SORT subroutine──────────────*/
strand_sort: procedure; parse arg x; y=
do while words(x)\==0; w=words(x)
do j=1 for w-1 /*any number | word out of order?*/
if word(x,j)>word(x,j+1) then do; w=j; leave; end
end /*j*/
y=merge(y,subword(x,1,w)); x=subword(x,w+1)
end /*while*/
return y
/*──────────────────────────────────MERGE subroutine────────────────────*/
merge: procedure; parse arg a.1,a.2; p=
do forever /*keep at it while 2 lists exist.*/
do i=1 for 2; w.i=words(a.i); end /*find number of entries in lists*/
if w.1*w.2==0 then leave /*if any list is empty, then stop*/
if word(a.1,w.1) <= word(a.2,1) then leave /*lists are now sorted?*/
if word(a.2,w.2) <= word(a.1,1) then return space(p a.2 a.1)
#=1+(word(a.1,1) >= word(a.2,1)); p=p word(a.#,1); a.#=subword(a.#,2)
end /*forever*/
return space(p a.1 a.2)

output when using the input of:   25 -9 30 1000 2000 3000

────────────────────────────────unsorted list────────────────────────────────
1000 2000 3000 9 0 3 -8 17 8 -2 4 0 -3 19 -1 3 1 8 27 14 20 2 -6 23 1 -8 -4 4

─────────────────────────────────sorted list─────────────────────────────────
-8 -8 -6 -4 -3 -2 -1 0 0 1 1 2 3 3 4 4 8 8 9 14 17 19 20 23 27 1000 2000 3000

The REXX program can also sort words as well as numbers.

output when using the input of:   24 -9 100 66 66 8.8 carp Carp

──────────────────────────────────────unsorted list───────────────────────────────────────
66 66 8.8 carp Carp 20 77 88 9 39 -5 10 12 80 87 26 61 87 94 73 27 49 35 95 81 76 40 13 72

───────────────────────────────────────sorted list────────────────────────────────────────
-5 8.8 9 10 12 13 20 26 27 35 39 40 49 61 66 66 72 73 76 77 80 81 87 87 88 94 95 Carp carp

Note that an   ASCII   computer will sort words differently than an   EBCDIC   machine.

The order of sorting on an   ASCII   machine is:   numbers, upperCase, lowerCase
The order of sorting on an EBCDIC machine is:   lowerCase, upperCase, numbers

[edit] Ruby

class Array
def strandsort
a = self.dup
result = []
until a.empty?
sublist = [a.shift]
a.each_with_index.each_with_object([]) { |(val, idx), remove|
next if val <= sublist.last
sublist << val
remove << idx
}.reverse_each {|idx| a.delete_at(idx)}
 
result.each_index do |idx|
break if sublist.empty?
result.insert(idx, sublist.shift) if sublist[0] < result[idx]
end
result += sublist
end
result
end
 
def strandsort!
replace(strandsort)
end
end
 
p [1, 6, 3, 2, 1, 7, 5, 3].strandsort

result

[1, 1, 2, 3, 3, 5, 6, 7]

[edit] Tcl

proc merge {listVar toMerge} {
upvar 1 $listVar v
set i [set j 0]
set out {}
while {$i<[llength $v] && $j<[llength $toMerge]} {
if {[set a [lindex $v $i]] < [set b [lindex $toMerge $j]]} {
lappend out $a
incr i
} else {
lappend out $b
incr j
}
}
# Done the merge, but will be one source with something left
# This will handle all that by doing a merge of the remnants onto the end
set v [concat $out [lrange $v $i end] [lrange $toMerge $j end]]
return
}
 
proc strandSort A {
set results {}
while {[llength $A]} {
set sublist [lrange $A 0 0]
# We build a list of items that weren't filtered rather than removing "in place"
# because this fits better with the way Tcl values work (the underlying data
# structure is an array, not a linked list).
set newA {}
foreach a [lrange $A 1 end] {
if {$a > [lindex $sublist end]} {
lappend sublist $a
} else {
lappend newA $a
}
}
set A $newA
merge results $sublist
}
return $results
}
 
puts [strandSort {3 1 5 4 2}]

[edit] Ursala

strand_sort "r" =  # parameterized by a relational predicate "r"
 
@NiX -+
 :-0 ~&B^?a\~&Y@a "r"?abh/~&alh2faltPrXPRC ~&arh2falrtPXPRC,
~&r->l ^|rlPlCrrPX/~& @hNCNXtX ~&r->lbx "r"?rllPXh/~&llPrhPlrPCXrtPX ~&rhPllPClrPXrtPX+-
demonstration code:
#cast %nL
 
x = (strand_sort nat-nleq) <3,1,5,4,2>
output:
<1,2,3,4,5>
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