Sorting algorithms/Selection sort

Sorting algorithms/Selection 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 comparing various sorts, see compare sorts.   For other sorting algorithms,   see sorting algorithms,   or:

O(n logn) sorts

Heap sort | Merge sort | Patience sort | Quick sort

O(n log²n) sorts
Shell Sort

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

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

In this task, the goal is to sort an array (or list) of elements using the Selection sort algorithm. It works as follows:

First find the smallest element in the array and exchange it with the element in the first position, then find the second smallest element and exchange it with the element in the second position, and continue in this way until the entire array is sorted. Its asymptotic complexity is O(n²) making it inefficient on large arrays.

Ada

with Ada.Text_IO; use Ada.Text_IO;

procedure Test_Selection_Sort is

  type Integer_Array is array (Positive range <>) of Integer;
  procedure Sort (A : in out Integer_Array) is
     Min  : Positive;
     Temp : Integer;
  begin
     for I in A'First..A'Last - 1 loop
        Min := I;
        for J in I + 1..A'Last loop
           if A (Min) > A (J) then
              Min := J;
           end if;
        end loop;
        if Min /= I then
           Temp    := A (I);
           A (I)   := A (Min);
           A (Min) := Temp;
        end if;
     end loop;
  end Sort;

  A : Integer_Array := (4, 9, 3, -2, 0, 7, -5, 1, 6, 8);

begin

  Sort (A);
  for I in A'Range loop
     Put (Integer'Image (A (I)) & " ");
  end loop;

end Test_Selection_Sort; Sample output:

-5 -2  0  1  3  4  6  7  8  9

ALGOL 68

Translation of: Ada

Works with: ALGOL 68 version Standard - no extensions to language used

Works with: ALGOL 68G version Any - tested with release mk15-0.8b.fc9.i386

Works with: ELLA ALGOL 68 version Any (with appropriate job cards) - tested with release 1.8.8d.fc9.i386

MODE DATA = REF CHAR;

PROC in place selection sort = (REF[]DATA a)VOID:
BEGIN
   INT min;
   DATA temp;
   FOR i FROM LWB a TO UPB a DO
      min := i;
      FOR j FROM i + 1 TO UPB a DO
         IF a [min] > a [j] THEN
            min := j
         FI
      OD;
      IF min /= i THEN
         temp    := a [i];
         a [i]   := a [min];
         a [min] := temp
      FI
   OD
END # in place selection sort #;
 
[32]CHAR data := "big fjords vex quick waltz nymph";
[UPB data]DATA ref data;  FOR i TO UPB data DO ref data[i] := data[i] OD;
in place selection sort(ref data);
FOR i TO UPB ref data DO print(ref data[i]) OD; print(new line);
print((data))

Output:

     abcdefghiijklmnopqrstuvwxyz
big fjords vex quick waltz nymph

C

#include <stdio.h>


int getminindex(int *a, int s, int b) {

 int i, min=a[s], mi=s;
 for(i=s; i < b; i++)
 {
   if ( a[i] < min ) { min = a[i]; mi = i; }
 }
 return mi;

}

void selectionsort(int *a, int s) {

 int i, t, mi;
 for(i=0; i<s ; i++)
 {
    mi = getminindex(a, i, s);
    t = a[i]; a[i] = a[mi]; a[mi] = t; 
 }

}

int main() {

  int ar[] = { 5, 200, 1, 65, 30, 99, 2, 0 };
  int i;
  
  selectionsort(ar, 8);
  for(i=0; i<8; i++)
  {
    printf("%d\n", ar[i]);
  }
  
  return 0;

}

Sample output

0
1
2
5
30
65
99
200

Forth

defer less?   ' < is less?

: least ( start end -- least )
  over cell+ do
    i @ over @ less? if drop i then
  cell +loop ;
: selection ( array len -- )
  cells over + tuck ( end start end )
  cell- swap do   ( end )
    i over least ( end least )
    i @ over @ i ! swap !
  cell +loop drop ;

create array 8 , 1 , 4 , 2 , 10 , 3 , 7 , 9 , 6 , 5 ,
 
array 10 selection
array 10 cells dump

Fortran

Works with: Fortran version 95 and later

PROGRAM SELECTION

 IMPLICIT NONE

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

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

CONTAINS

 SUBROUTINE Selection_sort(a)
   INTEGER, INTENT(IN OUT) :: a(:)
   INTEGER :: i, minIndex, temp

   DO i = 1, SIZE(a)-1
      minIndex = MINLOC(a(i:), 1) + i - 1
      IF (a(i) > a(minIndex)) THEN
         temp = a(i)
         a(i) = a(minIndex)
         a(minIndex) = temp
      END IF
   END DO
 END SUBROUTINE Selection_sort

END PROGRAM SELECTION Output:

Unsorted array:    4    9    3   -2    0    7   -5    1    6    8
Sorted array  :   -5   -2    0    1    3    4    6    7    8    9

Java

This algorithm sorts in place. The call sort(array) will rearrange the array and not create a new one. public static void sort(int[] nums){ for(int currentPlace = 0;currentPlace<nums.length-1;currentPlace++){ int smallest = Integer.MAX_VALUE; int smallestAt = currentPlace+1; for(int check = currentPlace+1; check<nums.length;check++){ if(nums[check]<smallest){ smallestAt = check; smallest = nums[check]; } } int temp = nums[currentPlace]; nums[currentPlace] = nums[smallestAt]; nums[smallestAt] = temp; } }