Quick Sort Program

Complexity and no. of swaps required

<syntaxhighlight lang="c" name="quicksort">

1. include <stdio.h>

void swap(int *a, int *b) { int temp = *a; *a = *b; *b = temp; }

void qsort(int a[], int start, int end) { int i, j, p; if(start >= end) return;

i = p = start, j = end; while(i < j)// Finds the no. of elements in the array < a[p] from the beginning and swaps with the no. of elements in the array greater than a[p] from the end { while(a[i] <= a[p] && i < end) i++; while(a[j] > a[p]) //( > ensures j never comes equal to p) j--; if(i < j) swap(&a[i], &a[j]); } swap(&a[j], &a[p]); qsort(a, start, j-1); qsort(a, j + 1, end); }

void printArray(int a[], int n) { int i; for(i = 0; i < n; i++) printf("%d ",a[i]); }

int main() { char str[20]; int num[100]; int i = 0; printf("Enter the numbers to sort (. to stop): "); while(1) { scanf("%s",str); if(str[0] == '.') break; sscanf(str, "%d", &num[i++]); } qsort(num, 0, i-1); printf("The sorted numbers are: "); printArray(num, i); printf("\n");

       return 0;

} </syntaxhighlight>

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