QuickSort using Random Pivoting.cpp

#include <cstdlib>
#include <iostream>
using namespace std;
 
// This function takes last element
// as pivot, places
// the pivot element at its correct
// position in sorted array, and
// places all smaller (smaller than pivot)
// to left of pivot and all greater
// elements to right of pivot
int partition(int arr[], int low, int high)
{
    // pivot
    int pivot = arr[high];
   
    // Index of smaller element
    int i = (low - 1);
 
    for (int j = low; j <= high - 1; j++)
    {
        // If current element is smaller
        // than or equal to pivot
        if (arr[j] <= pivot) {
 
            // increment index of
            // smaller element
            i++;
            swap(arr[i], arr[j]);
        }
    }
    swap(arr[i + 1], arr[high]);
    return (i + 1);
}
 
// Generates Random Pivot, swaps pivot with
// end element and calls the partition function
int partition_r(int arr[], int low, int high)
{
    // Generate a random number in between
    // low .. high
    srand(time(NULL));
    int random = low + rand() % (high - low);
 
    // Swap A[random] with A[high]
    swap(arr[random], arr[high]);
 
    return partition(arr, low, high);
}
 
/* The main function that implements
QuickSort
arr[] --> Array to be sorted,
low --> Starting index,
high --> Ending index */
void quickSort(int arr[], int low, int high)
{
    if (low < high) {
 
        /* pi is partitioning index,
        arr[p] is now
        at right place */
        int pi = partition_r(arr, low, high);
 
        // Separately sort elements before
        // partition and after partition
        quickSort(arr, low, pi - 1);
        quickSort(arr, pi + 1, high);
    }
}
 
/* 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 Code
int main()
{
    int arr[] = { 10, 7, 8, 9, 1, 5 };
    int n = sizeof(arr) / sizeof(arr[0]);
    quickSort(arr, 0, n - 1);
    printf("Sorted array: \n");
    printArray(arr, n);
    return 0;
}