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Sunday 17 March 2013

Selection Sort Algorithm And C Code

In computer science, a selection sort is a sorting algorithm, specifically an in-place comparison sort. It has O(n2) time complexity, making it inefficient on large lists, and generally performs worse than the similar Insertion sort. Selection sort is noted for its simplicity, and it has performance advantages over more complicated algorithms in certain situations, particularly where auxiliary memory is limited.
The algorithm divides the input list into two parts: the sublist of items already sorted, which is built up from left to right at the front (left) of the list, and the sublist of items remaining to be sorted that occupy the rest of the list. Initially, the sorted sublist is empty and the unsorted sublist is the entire input list. The algorithm proceeds by finding the smallest (or largest, depending on sorting order) element in the unsorted sublist, exchanging it with the leftmost unsorted element (putting it in sorted order), and moving the sublist boundaries one element to the right.


Worst case performanceО(n2)
Best case performanceО(n2)
Average case performanceО(n2)

Step-by-step example:

Selection Sort Algorithm And C Code

Here is an example of this sort algorithm sorting five elements:
64 25 12 22 11

11 25 12 22 64

11 12 25 22 64

11 12 22 25 64

11 12 22 25 64
(Nothing appears changed on this last line because the last 2 numbers were already in order.)
Selection sort can also be used on list structures that make add and remove efficient, such as a linked list. In this case it is more common to remove the minimum element from the remainder of the list, and then insert it at the end of the values sorted so far. For example:
64 25 12 22 11

11 64 25 12 22

11 12 64 25 22

11 12 22 64 25

11 12 22 25 64

Algorithm & Pseudo Code For Selection Sort:

/* Double-Click To Select Code */

/* a[0] to a[n-1] is the array to sort */
int i,j;
int iMin;
/* advance the position through the entire array */
/*   (could do j < n-1 because single element is also min element) */
for (j = 0; j < n-1; j++) {
    /* find the min element in the unsorted a[j .. n-1] */
    /* assume the min is the first element */
    iMin = j;
    /* test against elements after j to find the smallest */
    for ( i = j+1; i < n; i++) {
        /* if this element is less, then it is the new minimum */  
        if (a[i] < a[iMin]) {
            /* found new minimum; remember its index */
            iMin = i;
    /* iMin is the index of the minimum element. Swap it with the current position */
    if ( iMin != j ) {
        swap(a[j], a[iMin]);

C Program For Selection Sort:

/* Double-Click To Select Code */


int smallest(int arr[],int k,int n);
void sort(int arr[],int n);

void main()
 int arr[20],i,n,j,k;
 printf("\nEnter the number of elements in the array: ");

 printf("\nEnter the elements of the array");
 for(i=0 ; i < n ; i++)
  printf("\n arr[%d] = ",i);

 printf("\nThe sorted array is: \n");
 for(i=0 ; i < n ;  i++)

int smallest(int arr[],int k,int n)
 int pos=k,small=arr[k],i;
 return pos;

void sort(int arr[],int n)
 int k,pos,temp;
 for(k=0 ; k < n ; k++)

Output Of Program:

Selection Sort Algorithm And C Code

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This article uses material from the Wikipedia article Selection_sort which is released under the Creative Commons Attribution-Share-Alike License 3.0

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