quick_sort.cpp

#include <iostream>
#include <algorithm>
using namespace std;

int partition(int arr[], int low, int high)
{
   //take the last element as pivot
   int pivot = arr[high];
   int i = (low - 1); 

   //place pivot at its correct position and place all elements
   //smaller then the pivot to the left and all greater to the right
   for (int j = low; j <= high - 1; ++j)
   {
       if (arr[j] <= pivot)
       {
           i++; //increment index of smaller element
           swap(arr[i], arr[j]);
       }
   }
   swap(arr[i+1], arr[high]); //place the pivot in the correct position

   return (i+1);
}

void quick_sort(int arr[], int low, int high)
{
    if (low < high)
    {
        //pi is now at the correct place
        int pi = partition(arr, low, high);

        quick_sort(arr, low, pi-1);
        quick_sort(arr, pi+1, high);
    }
}

int main()
{
    int arr[] = {10, 7, 8, 9, 1, 5};
    int n = sizeof(arr) / sizeof(arr[0]);

    printf("quick sort:\n");
    quick_sort(arr, 0, n-1);

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

    return 0;
}