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Selection Sort in C Programming

Selection Sort in C Programming
Selection Sort in C Programming


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. 

Flow Chart for selection sort

Selection Sort - CodingTaggers
Implementation of selection sort in C Programming


#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;
}

 
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.

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