Sorting algorithms/Quicksort: Difference between revisions
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=={{header|Perl}}== |
=={{header|Perl}}== |
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<lang perl>sub quick_sort { |
<lang perl>sub quick_sort { |
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my @arr = @_; |
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my @less; |
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my @pivot_list; |
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my @more; |
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if ($# |
if ($#arr <= 0) { |
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return |
return @arr; |
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} else { |
} else { |
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$pivot = $arr |
$pivot = $arr[0]; |
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foreach my $i (@ |
foreach my $i (@arr) { |
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if ($i < $pivot) { |
if ($i < $pivot) { |
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push @ |
push @less, $i; |
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} elsif ($i > $pivot) { |
} elsif ($i > $pivot) { |
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push @ |
push @more, $i; |
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} else { |
} else { |
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push @ |
push @pivot_list, $i; |
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} |
} |
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} |
} |
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@less = quick_sort(@less); |
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@more = quick_sort(@more); |
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return |
return @less, @pivot_list, @more; |
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} |
} |
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} |
} |
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print join(' ', |
print join(' ', quick_sort(4, 65, 2, -31, 0, 99, 83, 782, 1)), "\n";</lang> |
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Output: |
Output: |
Revision as of 20:34, 12 March 2010
![Task](http://static.miraheze.org/rosettacodewiki/thumb/b/ba/Rcode-button-task-crushed.png/64px-Rcode-button-task-crushed.png)
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 comparing various sorts, see compare sorts.
For other sorting algorithms, see sorting algorithms, or:
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
In this task, the goal is to sort an array (or list) of elements using the Quicksort algorithm. The elements must have a strict weak order and the index of the array can be of any discrete type. For languages where this is not possible, sort an array of integers. The algorithm goes like this (from the wiki):
function quicksort(array) var list lessOrEqual, greater if length(array) ≤ 1 return array select a pivot value pivot for each x in array if x ≤ pivot then add x to lessOrEqual if x > pivot then add x to greater return concatenate(quicksort(lessOrEqual), concatenate(pivot, quicksort(greater)))
The "pivot" separates the dataset into two groups: those that are less than or equal to the value at the pivot and those that are greater than the pivot. An optimally selected pivot will result in partitions of equal length (or lengths differing by 1). The partitioning step may be thought of as a special sorting step using the attribute x ≤ pivot as the sort key, with possible values <true, false>. Quicksort's worst case time is O(n2),e.g., for a completely sorted set with the pivot chosen as the first or last element, but otherwise it is O(n * log n). Its average time is slightly faster than that of the merge sort in most cases, even though they are both O(n * log n) sorts.
Quicksort may be thought of as being situated at one end of the spectrum of divide-conquer algorithms, with Mergesort at the other end. In Quicksort, which some have called a conquer-divide algorithm, most of the work is done in the partitioning and recursive calls. The subsequent reassembly of the sorted segments involves trivial effort. In Mergesort, in contrast, the partitioning is done in a trivial way by splitting the input array in half. In Quicksort, every element in the first partition is less or equal to every element in the second partition. It is this property that makes the merge phase of Quicksort so trivial that it does not even need mentioning.
ActionScript
The functional programming way <lang actionscript>function quickSort (array:Array):Array {
if (array.length <= 1) return array;
var pivot:Number = array[Math.round(array.length / 2)];
return quickSort(array.filter(function (x:Number, index:int, array:Array):Boolean { return x < pivot; })).concat( array.filter(function (x:Number, index:int, array:Array):Boolean { return x == pivot; })).concat( quickSort(array.filter(function (x:Number, index:int, array:Array):Boolean { return x > pivot; })));
}</lang>
The faster way <lang actionscript>function quickSort (array:Array):Array {
if (array.length <= 1) return array;
var pivot:Number = array[Math.round(array.length / 2)];
var less:Array = []; var equal:Array = []; var greater:Array = [];
for each (var x:Number in array) { if (x < pivot) less.push(x); if (x == pivot) equal.push(x); if (x > pivot) greater.push(x); }
return quickSort(less).concat( equal).concat( quickSort(greater));
}</lang>
Ada
This example is implemented as a generic procedure. The procedure specification is: <lang ada>----------------------------------------------------------------------- -- Generic Quicksort procedure
generic
type Element_Type is private; type Index_Type is (<>); type Element_Array is array(Index_Type range <>) of Element_Type; with function "<" (Left, Right : Element_Type) return Boolean is <>; with function ">" (Left, Right : Element_Type) return Boolean is <>;
procedure Sort(Item : in out Element_Array);</lang> The procedure body deals with any discrete index type, either an integer type or an enumerated type. <lang ada>----------------------------------------------------------------------- -- Generic Quicksort procedure
procedure Sort (Item : in out Element_Array) is
procedure Swap(Left, Right : in out Element_Type) is Temp : Element_Type := Left; begin Left := Right; Right := Temp; end Swap; Pivot_Index : Index_Type; Pivot_Value : Element_Type; Right : Index_Type := Item'Last; Left : Index_Type := Item'First;
begin
if Item'Length > 1 then Pivot_Index := Index_Type'Val((Index_Type'Pos(Item'Last) + 1 + Index_Type'Pos(Item'First)) / 2); Pivot_Value := Item(Pivot_Index); loop Left := Item'First; Right := Item'Last; while Left < Item'Last and then Item(Left) < Pivot_Value loop Left := Index_Type'Succ(Left); end loop; while Right > Item'First and then Item(Right) > Pivot_Value loop Right := Index_Type'Pred(Right); end loop; exit when Left >= Right; Swap(Item(Left), Item(Right)); if Left < Item'Last and Right > Item'First then Left := Index_Type'Succ(Left); Right := Index_Type'Pred(Right); end if; end loop; if Right > Item'First then Sort(Item(Item'First..Right)); end if; if Left < Item'Last then Sort(Item(Left..Item'Last)); end if; end if;
end Sort;</lang> An example of how this procedure may be used is: <lang ada>with Sort; with Ada.Text_Io; with Ada.Float_Text_IO; use Ada.Float_Text_IO;
procedure Sort_Test is
type Days is (Mon, Tue, Wed, Thu, Fri, Sat, Sun); type Sales is array(Days range <>) of Float; procedure Sort_Days is new Sort(Float, Days, Sales); procedure Print(Item : Sales) is begin for I in Item'range loop Put(Item => Item(I), Fore => 5, Aft => 2, Exp => 0); end loop; end Print; Weekly_Sales : Sales := (Mon => 300.0, Tue => 700.0, Wed => 800.0, Thu => 500.0, Fri => 200.0, Sat => 100.0, Sun => 900.0);
begin
Print(Weekly_Sales); Ada.Text_Io.New_Line(2); Sort_Days(Weekly_Sales); Print(Weekly_Sales);
end Sort_Test;</lang>
ALGOL 68
From: http://en.wikibooks.org/wiki/Algorithm_implementation/Sorting/Quicksort#ALGOL_68 <lang algol68>PROC partition =(REF [] DATA array, PROC (REF DATA, REF DATA) BOOL cmp)INT: (
INT begin:=LWB array; INT end:=UPB array; WHILE begin < end DO WHILE begin < end DO IF cmp(array[begin], array[end]) THEN DATA tmp=array[begin]; array[begin]:=array[end]; array[end]:=tmp; GO TO break while decr end FI; end -:= 1 OD; break while decr end: SKIP; WHILE begin < end DO IF cmp(array[begin], array[end]) THEN DATA tmp=array[begin]; array[begin]:=array[end]; array[end]:=tmp; GO TO break while incr begin FI; begin +:= 1 OD; break while incr begin: SKIP OD; begin
);
PROC qsort=(REF [] DATA array, PROC (REF DATA, REF DATA) BOOL cmp)VOID: (
IF LWB array < UPB array THEN INT i := partition(array, cmp); PAR ( # remove PAR for single threaded sort # qsort(array[:i-1], cmp), qsort(array[i+1:], cmp) ) FI
);
MODE DATA = INT; PROC cmp=(REF DATA a,b)BOOL: a>b;
main:(
[]DATA const l=(5,4,3,2,1); [UPB const l]DATA l:=const l; qsort(l,cmp); printf(($g(3)$,l))
)</lang>
APL
<lang apl> qsort ← {1≥⍴⍵:⍵⋄e←⍵[?⍴⍵]⋄ (∇(⍵<e)/⍵) , ((⍵=e)/⍵) , ∇(⍵>e)/⍵}
qsort 1 3 5 7 9 8 6 4 2
1 2 3 4 5 6 7 8 9</lang>
Of course, in real APL applications, one would use ⍋ to sort (which will pick a sorting algorithm suited to the argument).
AutoHotkey
translated from python example <lang AutoHotkey>MsgBox % quicksort("8,4,9,2,1")
quicksort(list) {
StringSplit, list, list, `, If (list0 <= 1) Return list pivot := list1 Loop, Parse, list, `, { If (A_LoopField < pivot) less = %less%,%A_LoopField% Else If (A_LoopField > pivot) more = %more%,%A_LoopField% Else pivotlist = %pivotlist%,%A_LoopField% } StringTrimLeft, less, less, 1 StringTrimLeft, more, more, 1 StringTrimLeft, pivotList, pivotList, 1 less := quicksort(less) more := quicksort(more) Return less . pivotList . more
}</lang>
C
<lang c>void quick(int *left, int *right) {
if (right > left) { int pivot = left[(right-left)/2]; int *r = right, *l = left; do { while (*l < pivot) l++; while (*r > pivot) r--; if (l <= r) { int t = *l; *l++ = *r; *r-- = t; } } while (l <= r); quick(left, r); quick(l, right); }
} void sort(int *array, int length) {
quick(array, array+length-1);
}</lang>
C++
The following implements quicksort with a median-of-three pivot. As idiomatic in C++, the argument last is a one-past-end iterator. Note that this code takes advantage of std::partition, which is O(n). Also note that it needs a random-access iterator for efficient calculation of the median-of-three pivot (more exactly, for O(1) calculation of the iterator mid). <lang cpp>#include <iterator>
- include <algorithm> // for std::partition
- include <functional> // for std::less
// helper function for median of three template<typename T>
T median(T t1, T t2, T t3)
{
if (t1 < t2) { if (t2 < t3) return t2; else if (t1 < t3) return t3; else return t1; } else { if (t1 < t3) return t1; else if (t2 < t3) return t3; else return t2; }
}
// helper object to get <= from < template<typename Order> struct non_strict_op:
public std::binary_function<typename Order::second_argument_type, typename Order::first_argument_type, bool>
{
non_strict_op(Order o): order(o) {} bool operator()(typename Order::second_argument_type arg1, typename Order::first_argument_type arg2) const { return !order(arg2, arg1); }
private:
Order order;
};
template<typename Order> non_strict_op<Order> non_strict(Order o) {
return non_strict_op<Order>(o);
}
template<typename RandomAccessIterator,
typename Order> void quicksort(RandomAccessIterator first, RandomAccessIterator last, Order order)
{
if (first != last && first+1 != last) { typedef typename std::iterator_traits<RandomAccessIterator>::value_type value_type; RandomAccessIterator mid = first + (last - first)/2; value_type pivot = median(*first, *mid, *(last-1)); RandomAccessIterator split1 = std::partition(first, last, std::bind2nd(order, pivot)); RandomAccessIterator split2 = std::partition(split1, last, std::bind2nd(non_strict(order), pivot)); quicksort(first, split1, order); quicksort(split2, last, order); }
}
template<typename RandomAccessIterator>
void quicksort(RandomAccessIterator first, RandomAccessIterator last)
{
quicksort(first, last, std::less<typename std::iterator_traits<RandomAccessIterator>::value_type>());
}</lang>
A simpler version of the above that just uses the first element as the pivot and only does one "partition". <lang cpp>#include <iterator>
- include <algorithm> // for std::partition
- include <functional> // for std::less
template<typename RandomAccessIterator,
typename Order> void quicksort(RandomAccessIterator first, RandomAccessIterator last, Order order)
{
if (last - first > 1) { RandomAccessIterator split = std::partition(first+1, last, std::bind2nd(order, *first)); std::iter_swap(first, split-1); quicksort(first, split-1, order); quicksort(split, last, order); }
}
template<typename RandomAccessIterator>
void quicksort(RandomAccessIterator first, RandomAccessIterator last)
{
quicksort(first, last, std::less<typename std::iterator_traits<RandomAccessIterator>::value_type>());
}</lang>
Clojure
A very Haskell-like solution using list comprehensions and lazy evaluation. <lang lisp>(defn qsort [L]
(if (nil? L) '() (let [[pivot & L2] L] (lazy-cat (qsort (for [y L2 :when (< y pivot)] y)) (list pivot) (qsort (for [y L2 :when (>= y pivot)] y))))))</lang>
Another short version (using quasiquote):
<lang lisp>(defn qsort pvt & rs
(if pvt `(~@(qsort (filter #(< % pvt) rs)) ~pvt ~@(qsort (filter #(>= % pvt) rs)))))</lang>
Another, more readable version (no macros):
<lang lisp>(defn qsort pivot & xs
(when pivot (let [smaller #(< % pivot)] (lazy-cat (qsort (filter smaller xs))
[pivot] (qsort (remove smaller xs))))))</lang>
Common Lisp
The functional programming way
<lang lisp>(defun quicksort (list)
(if (<= (length list) 1) list (let ((pivot (first list)))
(append (quicksort (remove-if-not #'(lambda (x) (< x pivot)) list)) (remove-if-not #'(lambda (x) (= x pivot)) list) (quicksort (remove-if-not #'(lambda (x) (> x pivot)) list))))))</lang>
With macrolet
<lang lisp>(defun qs (list)
(if (< (length list) 2) list (macrolet ((pivot (test) `(remove (first list) list :test-not #',test))) (append (qs (pivot >)) (pivot =) (qs (pivot <))))))</lang>
In-place non-functional
<lang lisp>(defun quicksort (sequence)
(labels ((swap (a b) (rotatef (elt sequence a) (elt sequence b))) (sub-sort (left right) (when (< left right) (let ((pivot (elt sequence right)) (index left)) (loop for i from left below right when (<= (elt sequence i) pivot) do (swap i (prog1 index (incf index)))) (swap right index) (sub-sort left (1- index)) (sub-sort (1+ index) right))))) (sub-sort 0 (1- (length sequence))) sequence))</lang>
D
An implementation much similar to the C one is possible too, this is slower and simpler, derived from the Python one. This is a function template: <lang d>import std.stdio;
T[] quickSort(T)(T[] items) {
T[] less, more; if (items.length <= 1) return items; else { T pivot = items[0]; foreach(el; items[1 .. $]) if (el < pivot) less ~= el; else more ~= el; return quickSort(less) ~ pivot ~ quickSort(more); }
}
void main() {
auto a1 = [4, 65, 2, -31, 0, 99, 2, 83, 782, 1]; writefln(quickSort(a1)); auto a2 = [4.0,65.0,2.0,-31.0,0.0,99.0,2.0,83.0,782.0,1.0]; writefln(quickSort(a2));
}</lang>
E
<lang e>def quicksort := {
def swap(container, ixA, ixB) { def temp := container[ixA] container[ixA] := container[ixB] container[ixB] := temp }
def partition(array, var first :int, var last :int) { if (last <= first) { return } # Choose a pivot def pivot := array[def pivotIndex := (first + last) // 2] # Move pivot to end temporarily swap(array, pivotIndex, last) var swapWith := first # Scan array except for pivot, and... for i in first..!last { if (array[i] <= pivot) { # items ≤ the pivot swap(array, i, swapWith) # are moved to consecutive positions on the left swapWith += 1 } } # Swap pivot into between-partition position. # Because of the swapping we know that everything before swapWith is less # than or equal to the pivot, and the item at swapWith (since it was not # swapped) is greater than the pivot, so inserting the pivot at swapWith # will preserve the partition. swap(array, swapWith, last) return swapWith }
def quicksortR(array, first :int, last :int) { if (last <= first) { return } def pivot := partition(array, first, last) quicksortR(array, first, pivot - 1) quicksortR(array, pivot + 1, last) }
def quicksort(array) { # returned from block quicksortR(array, 0, array.size() - 1) }
}</lang>
Erlang
like haskell <lang erlang>qsort([]) -> []; qsort([X|Xs]) ->
qsort([ Y || Y <- Xs, Y < X]) ++ [X] ++ qsort([ Y || Y <- Xs, Y >= X]).</lang>
Factor
<lang factor>: qsort ( seq -- seq )
dup empty? [ unclip [ [ < ] curry partition [ qsort ] bi@ ] keep prefix append ] unless ;</lang>
Forth
<lang forth>defer lessthan ( a@ b@ -- ? ) ' < is lessthan
- mid ( l r -- mid ) over - 2/ -cell and + ;
- exch ( addr1 addr2 -- ) dup @ >r over @ swap ! r> swap ! ;
- partition ( l r -- l r r2 l2 )
2dup mid @ >r ( r: pivot ) 2dup begin swap begin dup @ r@ lessthan while cell+ repeat swap begin r@ over @ lessthan while cell- repeat 2dup <= if 2dup exch >r cell+ r> cell- then 2dup > until r> drop ;
- qsort ( l r -- )
partition swap rot \ 2over 2over - + < if 2swap then 2dup < if recurse else 2drop then 2dup < if recurse else 2drop then ;
- sort ( array len -- )
dup 2 < if 2drop exit then 1- cells over + qsort ;</lang>
Fortran
<lang fortran>MODULE Qsort_Module
IMPLICIT NONE
CONTAINS
RECURSIVE SUBROUTINE Qsort(a)
INTEGER, INTENT(IN OUT) :: a(:) INTEGER :: split IF(size(a) > 1) THEN CALL Partition(a, split) CALL Qsort(a(:split-1)) CALL Qsort(a(split:)) END IF
END SUBROUTINE Qsort
SUBROUTINE Partition(a, marker)
INTEGER, INTENT(IN OUT) :: a(:) INTEGER, INTENT(OUT) :: marker INTEGER :: left, right, pivot, temp pivot = (a(1) + a(size(a))) / 2 ! Average of first and last elements to prevent quadratic left = 0 ! behavior with sorted or reverse sorted data right = size(a) + 1 DO WHILE (left < right) right = right - 1 DO WHILE (a(right) > pivot) right = right-1 END DO left = left + 1 DO WHILE (a(left) < pivot) left = left + 1 END DO IF (left < right) THEN temp = a(left) a(left) = a(right) a(right) = temp END IF END DO IF (left == right) THEN marker = left + 1 ELSE marker = left END IF
END SUBROUTINE Partition
END MODULE Qsort_Module
PROGRAM Quicksort
USE Qsort_Module IMPLICIT NONE INTEGER, PARAMETER :: n = 100 INTEGER :: array(n) INTEGER :: i REAL :: x CALL RANDOM_SEED DO i = 1, n CALL RANDOM_NUMBER(x) array(i) = INT(x * 10000) END DO WRITE (*, "(A)") "array is :-" WRITE (*, "(10I5)") array CALL Qsort(array) WRITE (*,*) WRITE (*, "(A)") "sorted array is :-" WRITE (*,"(10I5)") array
END PROGRAM Quicksort</lang>
Haskell
The famous two-liner, reflecting the underlying algorithm directly: <lang haskell>qsort [] = [] qsort (x:xs) = qsort [y | y <- xs, y < x] ++ [x] ++ qsort [y | y <- xs, y >= x]</lang> A more efficient version, doing only one comparison per element: <lang haskell>import Data.List
qsort [] = [] qsort (x:xs) = qsort ys ++ x : qsort zs where (ys, zs) = partition (< x) xs</lang>
IDL
IDL has a powerful optimized sort() built-in. The following is thus merely for demonstration. <lang idl>function qs, arr
if (count = n_elements(arr)) lt 2 then return,arr pivot = total(arr) / count ; use the average for want of a better choice return,[qs(arr[where(arr le pivot)]),qs(arr[where(arr gt pivot)])] end</lang>
Example:
IDL> print,qs([3,17,-5,12,99]) -5 3 12 17 99
J
<lang j>sel=: 1 : 'x # ['
quicksort=: 3 : 0
if. 1 >: #y do. y else. (quicksort y <sel e),(y =sel e),quicksort y >sel e=.y{~?#y end.
)</lang>
See the Quicksort essay in the J Wiki for additional explanations and examples.
Java
<lang java5>public static <E extends Comparable<? super E>> List<E> quickSort(List<E> arr) {
if (arr.size() <= 1) return arr; E pivot = arr.getFirst(); //This pivot can change to get faster results
List<E> less = new LinkedList<E>(); List<E> pivotList = new LinkedList<E>(); List<E> more = new LinkedList<E>();
// Partition for (E i: arr) { if (i.compareTo(pivot) < 0) less.add(i); else if (i.compareTo(pivot) > 0) more.add(i); else pivotList.add(i); }
// Recursively sort sublists less = quickSort(less); more = quickSort(more);
// Concatenate results less.addAll(pivotList); less.addAll(more); return less;
}</lang>
JavaScript
<lang javascript>function sort(array, less) {
function swap(i, j) { var t=array[i]; array[i]=array[j]; array[j]=t }
function quicksort(left, right) {
if (left < right) {
var pivot = array[(left + right) >> 1]; var left_new = left, right_new = right;
do { while (less(array[left_new], pivot) left_new++; while (less(pivot, array[right_new]) right_new--; if (left_new <= right_new) swap(left_new++, right_new--); } while (left_new <= right_new);
quicksort(left, right_new); quicksort(left_new, right);
} }
quicksort(0, array.length-1);
return array;
}</lang>
The functional programming way
<lang javascript>Array.prototype.quick_sort = function () {
if (this.length <= 1) return this;
var pivot = this[Math.round(this.length / 2)];
return this.filter(function (x) { return x < pivot }).quick_sort().concat( this.filter(function (x) { return x == pivot })).concat( this.filter(function (x) { return x > pivot }).quick_sort());
}</lang>
Joy
<lang joy>DEFINE qsort ==
[small] [] [uncons [>] split] [swapd cons concat] binrec .</lang>
Logo
<lang logo>; quicksort (lists, functional)
to small? :list
output or [empty? :list] [empty? butfirst :list]
end to quicksort :list
if small? :list [output :list] localmake "pivot first :list output (sentence quicksort filter [? < :pivot] butfirst :list filter [? = :pivot] :list quicksort filter [? > :pivot] butfirst :list )
end
show quicksort [1 3 5 7 9 8 6 4 2]</lang> <lang logo>; quicksort (arrays, in-place)
to incr :name
make :name (thing :name) + 1
end to decr :name
make :name (thing :name) - 1
end to swap :i :j :a
localmake "t item :i :a setitem :i :a item :j :a setitem :j :a :t
end
to quick :a :low :high
if :high <= :low [stop] localmake "l :low localmake "h :high localmake "pivot item ashift (:l + :h) -1 :a do.while [ while [(item :l :a) < :pivot] [incr "l] while [(item :h :a) > :pivot] [decr "h] if :l <= :h [swap :l :h :a incr "l decr "h] ] [:l <= :h] quick :a :low :h quick :a :l :high
end to sort :a
quick :a first :a count :a
end
make "test {1 3 5 7 9 8 6 4 2} sort :test show :test</lang>
Lua
<lang lua> --in-place quicksort function quicksort(t, start, endi)
start, endi = start or 1, endi or #t --partition w.r.t. first element if(endi - start < 2) then return t end local pivot = start for i = start + 1, endi do if t[i] <= t[pivot] then local temp = t[pivot + 1] t[pivot + 1] = t[pivot] if(i == pivot + 1) then t[pivot] = temp else t[pivot] = t[i] t[i] = temp end pivot = pivot + 1 end end t = quicksort(t, start, pivot - 1) return quicksort(t, pivot + 1, endi)
end
--example print(unpack(quicksort{5, 2, 7, 3, 4, 7, 1})) </lang>
Lucid
[1] <lang lucid>qsort(a) = if eof(first a) then a else follow(qsort(b0),qsort(b1)) fi
where p = first a < a; b0 = a whenever p; b1 = a whenever not p; follow(x,y) = if xdone then y upon xdone else x fi where xdone = iseod x fby xdone or iseod x; end; end</lang>
M4
<lang M4>dnl return the first element of a list when called in the funny way seen below define(`arg1', `$1')dnl dnl dnl append lists 1 and 2 define(`append',
`ifelse(`$1',`()', `$2', `ifelse(`$2',`()', `$1', `substr($1,0,decr(len($1))),substr($2,1)')')')dnl
dnl dnl separate list 2 based on pivot 1, appending to left 3 and right 4, dnl until 2 is empty, and then combine the sort of left with pivot with dnl sort of right define(`sep',
`ifelse(`$2', `()', `append(append(quicksort($3),($1)),quicksort($4))', `ifelse(eval(arg1$2<=$1),1, `sep($1,(shift$2),append($3,(arg1$2)),$4)', `sep($1,(shift$2),$3,append($4,(arg1$2)))')')')dnl
dnl dnl pick first element of list 1 as pivot and separate based on that define(`quicksort',
`ifelse(`$1', `()', `()', `sep(arg1$1,(shift$1),`()',`()')')')dnl
dnl quicksort((3,1,4,1,5,9))</lang>
Output:
(1,1,3,4,5,9)
MATLAB
<lang Matlab>function f=quicksort(v) % v must be a column vector f = v; n=length(v); if(n > 1)
vl = min(f); vh = max(f); % min, max p = (vl+vh)*0.5; % pivot ia = find(f < p); ib = find(f == p); ic=find(f > p); f = [quicksort(f(ia)); f(ib); quicksort(f(ic))];
end return
N=256*256; v=rand(N,1); tic,u=quicksort(v); toc issorted(u)</lang>
MAXScript
<lang maxscript>fn quickSort arr = (
less = #() pivotList = #() more = #() if arr.count <= 1 then ( arr ) else ( pivot = arr[arr.count/2] for i in arr do ( case of ( (i < pivot): (append less i) (i == pivot): (append pivotList i) (i > pivot): (append more i) ) ) less = quickSort less more = quickSort more less + pivotList + more )
) a = #(4, 89, -3, 42, 5, 0, 2, 889) a = quickSort a</lang>
Nial
<lang nial>quicksort is fork [ >= [1 first,tally],
pass, link [ quicksort sublist [ < [pass, first], pass ], sublist [ match [pass,first],pass ], quicksort sublist [ > [pass,first], pass ] ]
]</lang>
Using it. <lang nial>|quicksort [5, 8, 7, 4, 3] =3 4 5 7 8</lang>
Nimrod
<lang python>proc QuickSort(list: seq[int]): seq[int] =
if len(list) == 0: return @[] var pivot = list[0] var left: seq[int] = @[] var right: seq[int] = @[] for i in low(list)+1..high(list): if list[i] <= pivot: left.add(list[i]) elif list[i] > pivot: right.add(list[i]) result = QuickSort(left) result.add(pivot) result.add(QuickSort(right))</lang>
Usage: <lang python>var sorted: seq[int] = QuickSort(@[5,2,1,6,2,3,1,2,123,21,54,6,1]) for i in items(sorted):
echo(i)</lang>
OCaml
<lang ocaml>let rec quicksort gt = function
| [] -> [] | x::xs -> let ys, zs = List.partition (gt x) xs in (quicksort gt ys) @ (x :: (quicksort gt zs))
let _ =
quicksort (>) [4; 65; 2; -31; 0; 99; 83; 782; 1]</lang>
Octave
(The MATLAB version works as is in Octave, provided that the code is put in a file named quicksort.m, and everything below the return must be typed in the prompt of course)
<lang octave>function f=quicksort(v) % v must be a column vector
f = v; n=length(v); if(n > 1) vl = min(f); vh = max(f); % min, max p = (vl+vh)*0.5; % pivot ia = find(f < p); ib = find(f == p); ic=find(f > p); f = [quicksort(f(ia)); f(ib); quicksort(f(ic))]; end
endfunction
N=30; v=rand(N,1); tic,u=quicksort(v); toc u</lang>
Oz
<lang oz>declare
fun {QuickSort Xs} case Xs of nil then nil [] Pivot|Xr then
fun {IsSmaller X} X < Pivot end
Smaller Larger in
{List.partition Xr IsSmaller ?Smaller ?Larger}
{Append {QuickSort Smaller} Pivot|{QuickSort Larger}} end end
in
{Show {QuickSort [3 1 4 1 5 9 2 6 5]}}</lang>
Perl
<lang perl>sub quick_sort {
my @arr = @_; my @less; my @pivot_list; my @more; if ($#arr <= 0) { return @arr; } else { $pivot = $arr[0]; foreach my $i (@arr) { if ($i < $pivot) { push @less, $i; } elsif ($i > $pivot) { push @more, $i; } else { push @pivot_list, $i; } } @less = quick_sort(@less); @more = quick_sort(@more); return @less, @pivot_list, @more; }
}
print join(' ', quick_sort(4, 65, 2, -31, 0, 99, 83, 782, 1)), "\n";</lang>
Output:
-31 0 1 2 4 65 83 99 782
In a more functional style: <lang perl>sub quicksort { @_ <= 1 ? @_ : do { my $pivot = pop; quicksort( grep {$_ <= $pivot} @_ ), $pivot, quicksort( grep {$_ > $pivot} @_ ) } }</lang> Accepting a sort function: <lang perl>sub quicksort (&@) { my $c = shift; @_ <= 1 ? @_ : do { local ($a, $b) = splice @_, rand @_, 1; my (@low, @high); for $b (@_) { $c->() <= 0 ? $high[@high] : $low[@low] = $b } quicksort( $c => @low ), $a, quicksort( $c => @high ) } }
print join ', ' => quicksort { $a <=> $b } 3, 5, 7, 1, -6, 12, 2;</lang>
PicoLisp
<lang lisp>(de quicksort (L)
(if (cdr L) (let Pivot (car L) (append (quicksort (filter '((A) (< A Pivot)) (cdr L))) (filter '((A) (= A Pivot)) L ) (quicksort (filter '((A) (> A Pivot)) (cdr L)))) ) L) )
</lang>
PL/I
<lang pli>DCL (T(20)) FIXED BIN(31); /* scratch space of length N */
QUICKSORT: PROCEDURE (A,AMIN,AMAX,N) RECURSIVE ;
DECLARE (A(*)) FIXED BIN(31); DECLARE (N,AMIN,AMAX) FIXED BIN(31) NONASGN; DECLARE (I,J,IA,IB,IC,PIV) FIXED BIN(31); DECLARE (P,Q) POINTER; DECLARE (AP(1)) FIXED BIN(31) BASED(P); IF(N <= 1)THEN RETURN; IA=0; IB=0; IC=N+1; PIV=(AMIN+AMAX)/2; DO I=1 TO N; IF(A(I) < PIV)THEN DO; IA+=1; A(IA)=A(I); END; ELSE IF(A(I) > PIV) THEN DO; IC-=1; T(IC)=A(I); END; ELSE DO; IB+=1; T(IB)=A(I); END; END; DO I=1 TO IB; A(I+IA)=T(I); END; DO I=IC TO N; A(I)=T(N+IC-I); END; P=ADDR(A(IC)); IC=N+1-IC; IF(IA > 1) THEN CALL QUICKSORT(A, AMIN, PIV-1,IA); IF(IC > 1) THEN CALL QUICKSORT(AP,PIV+1,AMAX, IC); RETURN;
END QUICKSORT;
MINMAX: PROC(A,AMIN,AMAX,N); DCL (AMIN,AMAX) FIXED BIN(31), (N,A(*)) FIXED BIN(31) NONASGN ; DCL (I,X,Y) FIXED BIN(31); AMIN=A(N); AMAX=AMIN; DO I=1 TO N-1; X=A(I); Y=A(I+1); IF (X < Y)THEN DO; IF (X < AMIN) THEN AMIN=X; IF (Y > AMAX) THEN AMAX=Y; END; ELSE DO; IF (X > AMAX) THEN AMAX=X; IF (Y < AMIN) THEN AMIN=Y; END; END; RETURN;
END MINMAX; CALL MINMAX(A,AMIN,AMAX,N); CALL QUICKSORT(A,AMIN,AMAX,N);</lang>
Prolog
<lang prolog>qsort( [], [] ). qsort( [X], [X] ). qsort( [H|U], S ) :- splitBy(H, U, L, R), qsort(L, SL), qsort(R, SR), combine(H, SL, SR, S).
% splitBy( H, U, LS, RS ) % True if LS = { L in U | L <= H }; RS = { R in U | R > H } splitBy( H, [], LS, RS). splitBy( H, [U|T], [U|LS], RS ) :- U =< H, splitBy(H, T, LS, RS). splitBy( H, [U|T], LS, [U|RS] ) :- U > H, splitBy(H, T, LS, RS).
% combine( H, L, R, S ) % True if S is L ++ [H] ++ R (in Haskell notation) combine( H, L, R, S ) :- append(L, [H|R], S).</lang>
PureBasic
<lang PureBasic>Procedure qSort(Array a(1), firstIndex, lastIndex)
Protected low, high, pivotValue
low = firstIndex high = lastIndex pivotValue = a((firstIndex + lastIndex) / 2) Repeat While a(low) < pivotValue low + 1 Wend While a(high) > pivotValue high - 1 Wend If low <= high Swap a(low), a(high) low + 1 high - 1 EndIf Until low > high If firstIndex < high qSort(a(), firstIndex, high) EndIf If low < lastIndex qSort(a(), low, lastIndex) EndIf
EndProcedure
Procedure quickSort(Array a(1))
qSort(a(),0,ArraySize(a()))
EndProcedure</lang>
Python
<lang python>def quickSort(arr):
less = [] pivotList = [] more = [] if len(arr) <= 1: return arr else: pivot = arr[0] for i in arr: if i < pivot: less.append(i) elif i > pivot: more.append(i) else: pivotList.append(i) less = quickSort(less) more = quickSort(more) return less + pivotList + more
a = [4, 65, 2, -31, 0, 99, 83, 782, 1] a = quickSort(a)</lang>
In a Haskell fashion -- <lang python>def qsort(L):
return (qsort([y for y in L[1:] if y < L[0]]) + L[:1] + qsort([y for y in L[1:] if y >= L[0]])) if len(L) > 1 else L</lang>
More readable, but still using list comprehensions: <lang python>def qsort(list):
if not list: return [] else: pivot = list[0] less = [x for x in list if x < pivot] more = [x for x in list[1:] if x >= pivot] return qsort(less) + [pivot] + qsort(more)</lang>
R
<lang R>qsort <- function(v) {
if ( length(v) > 1 ) { pivot <- (min(v) + max(v))/2.0 # Could also use pivot <- median(v) c(qsort(v[v < pivot]), v[v == pivot], qsort(v[v > pivot])) } else v
}
N <- 100 vs <- runif(N) system.time(u <- qsort(vs)) print(u)</lang>
Ruby
<lang ruby>class Array
def quick_sort return self if length <= 1 pivot = self[length / 2] find_all { |i| i < pivot }.quick_sort + find_all { |i| i == pivot } + find_all { |i| i > pivot }.quick_sort end
end</lang> or <lang ruby>class Array
def quick_sort return self if length <= 1 pivot = self[0] less, greatereq = self[1..-1].partition { |x| x < pivot } less.quick_sort + [pivot] + greatereq.quick_sort end
end</lang>
Scala
I'll show a progression on genericity here.
First, a quick sort of a list of integers:
<lang scala>def quicksortInt(coll: List[Int]): List[Int] =
if (coll.isEmpty) { coll } else { val (smaller, bigger) = coll.tail partition (_ < coll.head) quicksortInt(smaller) ::: coll.head :: quicksortInt(bigger) }</lang>
Next, a quick sort of a list of some type T, given a lessThan function:
<lang scala>def quicksortFunc[T](coll: List[T], lessThan: (T, T) => Boolean): List[T] =
if (coll.isEmpty) { coll } else { val (smaller, bigger) = coll.tail partition (lessThan(_, coll.head)) quicksortFunc(smaller, lessThan) ::: coll.head :: quicksortFunc(bigger, lessThan) }</lang>
To take advantage of known orderings, a quick sort of a list of some type T, for which exists an implicit (or explicit) Ordered[T]:
<lang scala>def quicksortOrd[T <% Ordered[T]](coll: List[T]): List[T] =
if (coll.isEmpty) { coll } else { val (smaller, bigger) = coll.tail partition (_ < coll.head) quicksortOrd(smaller) ::: coll.head :: quicksortOrd(bigger) }</lang>
That last one could have worked with Ordering, but Ordering is Java, and doesn't have the less than operator. Ordered is Scala-specific, and provides it.
What hasn't changed in all these examples is that I'm ordering a list. It is possible to write a generic quicksort in Scala, which will order any kind of collection. To do so, however, requires that the type of the collection, itself, be made a parameter to the function. Let's see it below, and then remark upon it:
<lang scala>def quicksort
[T, CC[X] <: Traversable[X] with TraversableLike[X, CC[X]]] // My type parameters (coll: CC[T]) // My explicit parameter (implicit o: T => Ordered[T], cbf: CanBuildFrom[CC[T], T, CC[T]]) // My implicit parameters : CC[T] = // My return type if (coll.isEmpty) { coll } else { val (smaller, bigger) = coll.tail partition (_ < coll.head) quicksort(smaller) ++ coll.companion(coll.head) ++ quicksort(bigger) }</lang>
That will only work starting with Scala 2.8. The type of our collection is "CC", and, by providing CC[X] as a type parameter to TraversableLike, we ensure CC is capable of returing instances of type CC. Traversable is the base type of all collections, and TraversableLike is a trait which contains the implementation of most Traversable methods.
We need another parameter, though, which is a factory capable of building a CC collection. That is being passed implicitly, so callers to this method do not need to provide them, as the collection they are using should already provide such implicit. Because we need that implicit, then we need to ask for the "T => Ordered[T]" as well, as the "T <% Ordered[T]" which provides it cannot be used in conjunction with implicit parameters.
The body of the function is pretty much the same of the body for the list variant, but using "++" instead of list-specific methods "::" and ":::", and using "coll.companion" to build a collection out of one element.
Scheme
<lang scheme>(define (split-by l p)
(let loop ((low (list)) (high (list)) (l l)) (if (null? l) (cons low high) (if (p (car l)) (loop low (cons (car l) high) (cdr l)) (loop (cons (car l) low) high (cdr l))))))
(define (quicksort l gt?)
(let q ((l l)) (if (null? l) l (let ((s (split-by (cdr l) (lambda (x) (gt? x (car l)))))) (append (q (car s)) (list (car l)) (q (cdr s))))))) (quicksort (list 1 3 5 7 9 8 6 4 2) >)</lang>
Seed7
<lang seed7>const proc: quickSort (inout array elemType: arr, in integer: left, in integer: right) is func
local var elemType: compare_elem is elemType.value; var integer: less_idx is 0; var integer: greater_idx is 0; var elemType: help is elemType.value; begin if right > left then compare_elem := arr[right]; less_idx := pred(left); greater_idx := right; repeat repeat incr(less_idx); until arr[less_idx] >= compare_elem; repeat decr(greater_idx); until arr[greater_idx] <= compare_elem or greater_idx = left; if less_idx < greater_idx then help := arr[less_idx]; arr[less_idx] := arr[greater_idx]; arr[greater_idx] := help; end if; until less_idx >= greater_idx; arr[right] := arr[less_idx]; arr[less_idx] := compare_elem; quickSort(arr, left, pred(less_idx)); quickSort(arr, succ(less_idx), right); end if; end func;
const proc: quickSort (inout array elemType: arr) is func
begin quickSort(arr, 1, length(arr)); end func;</lang>
Original source: [2]
SETL
In-place sort (looks much the same as the C version) <lang SETL>a := [2,5,8,7,0,9,1,3,6,4]; qsort(a); print(a);
proc qsort(rw a);
if #a > 1 then pivot := a(#a div 2 + 1); l := 1; r := #a; (while l < r) (while a(l) < pivot) l +:= 1; end; (while a(r) > pivot) r -:= 1; end; swap(a(l), a(r)); end; qsort(a(1..l-1)); qsort(a(r+1..#a)); end if;
end proc;
proc swap(rw x, rw y);
[y,x] := [x,y];
end proc;</lang>
Copying sort using comprehensions:
<lang SETL>a := [2,5,8,7,0,9,1,3,6,4]; print(qsort(a));
proc qsort(a);
if #a > 1 then pivot := a(#a div 2 + 1); a := qsort([x in a | x < pivot]) + [x in a | x = pivot] + qsort([x in a | x > pivot]); end if; return a;
end proc;</lang>
Standard ML
<lang sml>fun quicksort [] = []
| quicksort (x::xs) = let val (left, right) = List.partition (fn y => y<x) xs in quicksort left @ [x] @ quicksort right end</lang>
Tcl
<lang tcl>package require Tcl 8.5
proc quicksort {m} {
if {[llength $m] <= 1} { return $m } set pivot [lindex $m 0] set less [set equal [set greater [list]]] foreach x $m { lappend [expr {$x < $pivot ? "less" : $x > $pivot ? "greater" : "equal"}] $x } return [concat [quicksort $less] $equal [quicksort $greater]]
}
puts [quicksort {8 6 4 2 1 3 5 7 9}] ;# => 1 2 3 4 5 6 7 8 9</lang>
UnixPipes
<lang bash>split() {
(while read n ; do test $1 -gt $n && echo $n > $2 || echo $n > $3 done)
}
qsort() {
(read p; test -n "$p" && ( lc="1.$1" ; gc="2.$1" split $p >(qsort $lc >$lc) >(qsort $gc >$gc); cat $lc <(echo $p) $gc rm -f $lc $gc; ))
}
cat to.sort | qsort</lang>
Ursala
The distributing bipartition operator, *|, is useful for this algorithm. The pivot is chosen as the greater of the first two items, this being the least sophisticated method sufficient to ensure termination. The quicksort function is a higher order function parameterized by the relational predicate p, which can be chosen appropriately for the type of items in the list being sorted. This example demonstrates sorting a list of natural numbers.
<lang Ursala>#import nat
quicksort "p" = ~&itB^?a\~&a ^|WrlT/~& "p"*|^\~& "p"?hthPX/~&th ~&h
- cast %nL
example = quicksort(nleq) <694,1377,367,506,3712,381,1704,1580,475,1872></lang> output:
<367,381,475,506,694,1377,1580,1704,1872,3712>
V
<lang v>[qsort
[joinparts [p [*l1] [*l2] : [*l1 p *l2]] view]. [split_on_first uncons [>] split]. [small?] [] [split_on_first [l1 l2 : [l1 qsort l2 qsort joinparts]] view i] ifte].</lang>
The way of joy (using binrec) <lang v>[qsort
[small?] [] [uncons [>] split] [[p [*l] [*g] : [*l p *g]] view]</lang> binrec].
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