几种排序算法：堆排序、快速排序，归并排序

下面是几种算法的C++代码实现与对比：

#include <cstdio>
#include <algorithm>
#include <ctime>
using namespace std;
//------------------------快速排序----------------------------
void quick_sort(int s[], int l, int r)
{
    if (l < r)
    {
        int i = l, j = r, x = s[l];
        while (i < j)
        {
            while(i < j && s[j] >= x) // 从右向左找第一个小于x的数
                j--;  
            if(i < j) 
                s[i++] = s[j];
 
            while(i < j && s[i] < x) // 从左向右找第一个大于等于x的数
                i++;  
            if(i < j) 
                s[j--] = s[i];
        }
        s[i] = x;
        quick_sort(s, l, i - 1); // 递归调用 
        quick_sort(s, i + 1, r);
    }
}
//------------------------归并排序----------------------------
//将有二个有序数列a[first...mid]和a[mid...last]合并。
void mergearray(int a[], int first, int mid, int last, int temp[])
{
    int i = first, j = mid + 1;
    int m = mid,   n = last;
    int k = 0;
 
    while (i <= m && j <= n)
    {
        if (a[i] < a[j])
            temp[k++] = a[i++];
        else
            temp[k++] = a[j++];
    }
 
    while (i <= m)
        temp[k++] = a[i++];
 
    while (j <= n)
        temp[k++] = a[j++];
 
    for (i = 0; i < k; i++)
        a[first + i] = temp[i];
}
void mergesort(int a[], int first, int last, int temp[])
{
    if (first < last)
    {
        int mid = (first + last) / 2;
        mergesort(a, first, mid, temp);    //左边有序
        mergesort(a, mid + 1, last, temp); //右边有序
        mergearray(a, first, mid, last, temp); //再将二个有序数列合并
    }
}
bool MergeSort(int a[], int n)
{
    int *p = new int[n];
    if (p == NULL)
        return false;
    mergesort(a, 0, n - 1, p);
    return true;
}
//------------------------堆排序---------------------------
inline void Swap(int &a, int &b)
{
    int c = a;
    a = b;
    b = c;
}
//建立最小堆
//  从i节点开始调整,n为节点总数 从0开始计算 i节点的子节点为 2*i+1, 2*i+2
void MinHeapFixdown(int a[], int i, int n)
{
    int j, temp;
 
    temp = a[i];
    j = 2 * i + 1;
    while (j < n)
    {
        if (j + 1 < n && a[j + 1] < a[j]) //在左右孩子中找最小的
            j++;
 
        if (a[j] >= temp)
            break;
 
        a[i] = a[j];     //把较小的子结点往上移动,替换它的父结点
        i = j;
        j = 2 * i + 1;
    }
    a[i] = temp;
}
//建立最小堆
void MakeMinHeap(int a[], int n)
{
    for (int i = n / 2 - 1; i >= 0; i--)
        MinHeapFixdown(a, i, n);
}
void MinheapsortTodescendarray(int a[], int n)
{
    for (int i = n - 1; i >= 1; i--)
    {
        Swap(a[i], a[0]);
        MinHeapFixdown(a, 0, i);
    }
}
const int MAXN = 5000000;
int a[MAXN];
int b[MAXN], c[MAXN], d[MAXN];
int main()
{
    int i;
    srand(time(NULL));
    for (i = 0; i < MAXN; ++i)
        a[i] = rand() * rand(); //注rand()产生的数在0到0x7FFF之间
 
    for (i = 0; i < MAXN; ++i)
        d[i] = c[i] = b[i] = a[i];
 
    clock_t ibegin, iend;
 
    printf("--当前数据量为%d\n", MAXN);
    //快速排序
    printf("快速排序:  ");
    ibegin = clock();
    quick_sort(a, 0, MAXN - 1);
    iend = clock();
    printf("%d毫秒\n", iend - ibegin);
 
    
    //归并排序
    printf("归并排序:  ");
    ibegin = clock();
    MergeSort(b, MAXN);
    iend = clock();
    printf("%d毫秒\n", iend - ibegin);
 
    //堆排序
    printf("堆排序:  ");
    ibegin = clock();
    MakeMinHeap(c, MAXN);
    MinheapsortTodescendarray(c, MAXN);
    iend = clock();
    printf("%d毫秒\n", iend - ibegin);
 
    //STL中的堆排序
    printf("STL中的堆排序: ");    
    ibegin = clock();
    make_heap(d, d + MAXN);
    sort_heap(d, d + MAXN);
    iend = clock();
    printf("%d毫秒\n", iend - ibegin);
    return 0;
}