排序算法之----快速排序

#include <stdio.h>
#include <stdlib.h>

void print(int a[], int num);
int Partion3(int k[], int low, int hight);
int Partion(int k[], int low, int hight);
void Qsort(int k[], int low, int hight);

void swap(int k[], int a, int b)
{
    int tmp = k[a];
    k[a] = k[b];
    k[b] = tmp;
}

//快速排序
//基本思想：找基准点二分法递归
void QuickSort(int k[], int n)
{
    Qsort(k, 0, n - 1);
}

void Qsort(int k[], int low, int hight)
{
    int point;
    if (low < hight)
    {
        point = Partion3(k, low, hight);
        Qsort(k, low, point - 1);
        Qsort(k, point + 1, hight);
    }
}

int Partion(int k[], int low, int hight)
{
    int point;
    point = k[low];
    while (low < hight)
    {
        //右边的全部大于point
        while ((low < hight) && k[hight] >= point)
        {
            hight--;
        }
        //交换的目的是将小与point的放入low
        swap(k, low, hight);
        //左边的全部小于point
        while ((low < hight) && k[low] <= point)
        {
            low++;
        }
        //交换的目的是将大于point的放入hight
        swap(k, low, hight);
    }
    return low;
}

//快速排序的优化
//1.优化基准点：3数取中法
int Partion2(int k[], int low, int hight)
{
    int point;
    point = k[low];
    int m = low + (hight - low) / 2;
    if (k[low] > k[hight])
    {
        swap(k, low, hight);
    }
    if (k[m] > k[hight])
    {
        swap(k, m, hight);
    }
    //使得low为中间值
    if (k[m] > k[low])
    {
        swap(k, m, hight);
    }

    while (low < hight)
    {
        //右边的全部大于point
        while ((low < hight) && k[hight] >= point)
        {
            hight--;
        }
        //交换的目的是将小与point的放入low
        swap(k, low, hight);
        //左边的全部小于point
        while ((low < hight) && k[low] <= point)
        {
            low++;
        }
        //交换的目的是将大于point的放入hight
        swap(k, low, hight);
    }
    return low;
}

//2. 优化交换
int Partion3(int k[], int low, int hight)
{
    int point;
    point = k[low];
    while (low < hight)
    {
        //右边的全部大于point
        while ((low < hight) && k[hight] >= point)
        {
            hight--;
        }
        //交换的目的是将小与point的放入low
        k[low] = k[hight];
        //左边的全部小于point
        while ((low < hight) && k[low] <= point)
        {
            low++;
        }
        //交换的目的是将大于point的放入hight
        k[hight] = k[low];
    }
    k[low] = point;
    return low;
}

//3. 数目小于7使用插入排序
//4. 优化递归操作：尾递归会被编译器优化，不会开辟栈

void print(int a[], int num)
{
    int i = 0;
    for (i = 0; i < num; i++)
    {
        printf("%d ", a[i]);
    }
    printf("
");
}

int main()
{
    int a[10] = { 2, 3, 56, 1, 4, 7, 8, 94, 3, 10 };
    print(a, 10);

    QuickSort(a, 10);
    printf("快速排序
");
    print(a, 10);

    return system("pause");
}