快速排序【代码】

思路参考《算法导论》P95

这里有位老哥的文章写的挺形象的呀

http://developer.51cto.com/art/201403/430986.htm

我是参照书上实现的，觉得挺简单的

-------------------------------------------------------代码-------------------------------------------------------

// QUICKSORT.cpp: 定义控制台应用程序的入口点。
//

#include "stdafx.h"
#include <iostream>
#include <random>

using namespace std;

int PARTITION(int *A, int p, int r)
{
    int x = A[r];
    int i = p - 1;
    int temp;
    for (int j = p; j < r; j++)
    {
        if (A[j] <= x)
        {
            i++;
            temp = A[i];
            A[i] = A[j];
            A[j] = temp;
        }
    }
    temp = A[i+1];
    A[i+1] = A[r];
    A[r] = temp;
    return i+1;
}

int QUICKSORT(int *A,int p,int r)
{
    if (p < r)
    {
        int q = PARTITION(A,p,r);
        QUICKSORT(A, p, q - 1);
        QUICKSORT(A, q + 1, r);
    }
    return 0;
}

//------------------------------随机化版本--------------------------------

int RANDOM_PARTITION(int *A, int p, int r)
{
    uniform_int_distribution<unsigned> u(p,r);
    default_random_engine e;
    int i = u(e);//生成[p,r]之间的随机数
    int temp = A[i];
    A[i] = A[r];
    A[r] = temp;
    return PARTITION(A,p,r);
}

int RANDOM_QUICKSORT(int *A, int p, int r)
{
    if (p < r)
    {
        int q = RANDOM_PARTITION(A, p, r);
        RANDOM_QUICKSORT(A, p, q - 1);
        RANDOM_QUICKSORT(A, q + 1, r);
    }
    return 0;
}


int main()
{
    int A[] = { 2,8,7,1,3,5,6,4 };
    int B[] = { 2,8,7,1,3,5,6,4 };
    for (auto c : A)
        cout << c << ends;
    cout << endl;

    QUICKSORT(A,0,7);
    for (auto c : A)
        cout << c << ends;
    cout << endl;

    RANDOM_QUICKSORT(B, 0, 7);
    for (auto c : B)
        cout << c << ends;
    cout << endl;
    return 0;
}

运行结果：