programming-examples/c/Search_Sorting/C Program to Implement Quick Sort Using Randomization.c

/*
 * C Program to Implement Quick Sort Using Randomization
 */
#include <stdio.h>
#include <stdlib.h>
#define MAX 100
void random_shuffle(int arr[])
{
    srand(time(NULL));
    int i, j, temp;
    for (i = MAX - 1; i > 0; i--)
        {
            j = rand()%(i + 1);
            temp = arr[i];
            arr[i] = arr[j];
            arr[j] = temp;
        }
}

void swap(int *a, int *b)
{
    int temp;
    temp = *a;
    *a = *b;
    *b = temp;
}
int partion(int arr[], int p, int r)
{
    int pivotIndex = p + rand()%(r - p + 1); //generates a random number as a pivot
    int pivot;
    int i = p - 1;
    int j;
    pivot = arr[pivotIndex];
    swap(&arr[pivotIndex], &arr[r]);
    for (j = p; j < r; j++)
        {
            if (arr[j] < pivot)
                {
                    i++;
                    swap(&arr[i], &arr[j]);
                }
        }
    swap(&arr[i+1], &arr[r]);
    return i + 1;
}

void quick_sort(int arr[], int p, int q)
{
    int j;
    if (p < q)
        {
            j = partion(arr, p, q);
            quick_sort(arr, p, j-1);
            quick_sort(arr, j+1, q);
        }
}
int main()
{
    int i;
    int arr[MAX];
    for (i = 0; i < MAX; i++)
        arr[i] = i;
    random_shuffle(arr); //To randomize the array
    quick_sort(arr, 0, MAX-1); //function to sort the elements of array
    for (i = 0; i < MAX; i++)
        printf("%d \n", arr[i]);
    return 0;
}