quick_sort

Average-case running time: O(nlgn)
Worst-case running time: O(n^2)

There is also randomized version of quick_sort

The original partition algorithm is hoare_partition

 

 

/////////////////////Test Code/////////////////////
#include "stdafx.h"
#include "stdlib.h"
#include <time.h>
#include "basic_algorithm.h"
#include <iostream>
using namespace std;


int _tmain(int argc, _TCHAR* argv[])
{
    
    srand((unsigned)time(NULL));
    int *arr = new int[20];
    for(int i = 0; i < 20; ++i)
    {
        arr[i] = rand() % 30;
    }
    enzo::quick_sort(arr,20);
    for(int i = 0; i < 20; ++i)
    {
        cout << arr[i] << " ";
    }
    cout << endl;
    system("pause");
    return 0;
}

//////////////////Source Code//////////////////////
    template<typename _T>
    int partition(_T *arr, int from, int to)
    {
        int j = from;
        int k = from;
        _T temp = arr[to];
        while(k < to)
        {
            if(arr[k] < temp)
            {
                ez_swap(arr[j],arr[k]);
                ++j;
                ++k;
            }
            else
            {
                ++k;
            }
        }
        if(arr[to] < arr[j])
        {
            ez_swap(arr[to], arr[j]);
        }
        return j;
    }
    template<typename _T>
    void quick_sort(_T *arr, int from, int to)
    {
        if(from < to)
        {
            int mid = partition(arr, from, to);
            quick_sort(arr, from, mid - 1);
            quick_sort(arr, mid + 1, to);
        }
    }

    template<typename _T>
    void quick_sort(_T *arr, int n)
    {
        quick_sort(arr, 0, n-1);
    }