Selection Sort

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The selection sort algorithm sorts an array by repeatedly finding the minimum element (considering ascending order) from unsorted part and putting it at the beginning. The algorithm maintains two subarrays in a given array.

1) The subarray which is already sorted.
2) Remaining subarray which is unsorted.

In every iteration of selection sort, the minimum element (considering ascending order) from the unsorted subarray is picked and moved to the sorted subarray.


Following example explains the above steps:


arr[] = 64 25 12 22 11

// Find the minimum element in arr[0...4]
// and place it at beginning
11 25 12 22 64

// Find the minimum element in arr[1...4]
// and place it at beginning of arr[1...4]
11 12 25 22 64

// Find the minimum element in arr[2...4]
// and place it at beginning of arr[2...4]
11 12 22 25 64

// Find the minimum element in arr[3...4]
// and place it at beginning of arr[3...4]
11 12 22 25 64 

C/C++

// C program for implementation of selection sort
#include <stdio.h>
  
void swap(int *xp, int *yp)
    int temp = *xp;
    *xp = *yp;
    *yp = temp;
  
void selectionSort(int arr[], int n)
    int i, j, min_idx;
  
    // One by one move boundary of unsorted subarray
    for (i = 0; i < n-1; i++)
    {
        // Find the minimum element in unsorted array
        min_idx = i;
        for (j = i+1; j < n; j++)
          if (arr[j] < arr[min_idx])
            min_idx = j;
  
        // Swap the found minimum element with the first element
        swap(&arr[min_idx], &arr[i]);
    }
  
/* Function to print an array */
void printArray(int arr[], int size)
    int i;
    for (i=0; i < size; i++)
        printf("%d ", arr[i]);
    printf("\n");
  
// Driver program to test above functions
int main()
    int arr[] = {64, 25, 12, 22, 11};
    int n = sizeof(arr)/sizeof(arr[0]);
    selectionSort(arr, n);
    printf("Sorted array: \n");
    printArray(arr, n);
    return 0;

Python

# Python program for implementation of Selection
import sys
A = [64, 25, 12, 22, 11]
  
# Traverse through all array elements
for i in range(len(A)):
      
    # Find the minimum element in remaining 
    # unsorted array
    min_idx = i
    for j in range(i+1, len(A)):
        if A[min_idx] > A[j]:
            min_idx = j
              
    # Swap the found minimum element with 
    # the first element        
    A[i], A[min_idx] = A[min_idx], A[i]
  
# Driver code to test above
print ("Sorted array")
for i in range(len(A)):
    print("%d" %A[i]), 

Java

// Java program for implementation of Selection Sort
class SelectionSort
    void sort(int arr[])
    {
        int n = arr.length;
  
        // One by one move boundary of unsorted subarray
        for (int i = 0; i < n-1; i++)
        {
            // Find the minimum element in unsorted array
            int min_idx = i;
            for (int j = i+1; j < n; j++)
                if (arr[j] < arr[min_idx])
                    min_idx = j;
  
            // Swap the found minimum element with the first
            // element
            int temp = arr[min_idx];
            arr[min_idx] = arr[i];
            arr[i] = temp;
        }
    }
  
    // Prints the array
    void printArray(int arr[])
    {
        int n = arr.length;
        for (int i=0; i<n; ++i)
            System.out.print(arr[i]+" ");
        System.out.println();
    }
  
    // Driver code to test above
    public static void main(String args[])
    {
        SelectionSort ob = new SelectionSort();
        int arr[] = {64,25,12,22,11};
        ob.sort(arr);
        System.out.println("Sorted array");
        ob.printArray(arr);
    }
/* This code is contributed by Rajat Mishra*/

C#

// C# program for implementation 
// of Selection Sort
using System;
  
    static void sort(int []arr)
    {
        int n = arr.Length;
  
        // One by one move boundary of unsorted subarray
        for (int i = 0; i < n - 1; i++)
        {
            // Find the minimum element in unsorted array
            int min_idx = i;
            for (int j = i + 1; j < n; j++)
                if (arr[j] < arr[min_idx])
                    min_idx = j;
  
            // Swap the found minimum element with the first
            // element
            int temp = arr[min_idx];
            arr[min_idx] = arr[i];
            arr[i] = temp;
        }
    }
  
    // Prints the array
    static void printArray(int []arr)
    {
        int n = arr.Length;
        for (int i=0; i<n; ++i)
            Console.Write(arr[i]+" ");
        Console.WriteLine();
    }
  
    // Driver code 
    public static void Main()
    {
        int []arr = {64,25,12,22,11};
        sort(arr);
        Console.WriteLine("Sorted array");
        printArray(arr);
    }
  
// This code is contributed by Sam007

Output:

Sorted array:
11 12 22 25 64

Time Complexity: O(n2) as there are two nested loops.

Auxiliary Space: O(1)
The good thing about selection sort is it never makes more than O(n) swaps and can be useful when memory write is a costly operation.


Exercise :
Sort an array of strings using Selection Sort

Stability : The default implementation is not stable. However it can be made stable. Please see stable selection sort for details.

In Place : Yest, it does not require extra space.

 

Snapshots:
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Other Sorting Algorithms on GeeksforGeeks/GeeksQuiz:

  • Bubble Sort
  • Insertion Sort
  • Merge Sort
  • Heap Sort
  • QuickSort
  • Radix Sort
  • Counting Sort
  • Bucket Sort
  • ShellSort
  • Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above


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