今天，我學習了一些優化快速排序的方法。
附上程式碼：
(優化前的程式碼為被註釋掉的程式碼，優化後的程式碼我也用中文註釋加以說明了)

#include <stdio.h>
void swap(int *a, int *b);

void QuickSort(int *a, int low, int high)
{
    //if(low < high)
    while(low < high)   //優化："尾遞迴",減少遞迴深度
    {
        int pivot = Partition(a, low, high);
        QuickSort(a, low, pivot-1
 
);
        //QuickSort(a, pivot+1, high);
        low = pivot+1;  //優化："尾遞迴",減少遞迴深度
    }
}

int Partition(int *a, int low, int high)
{
    int mid = low + (high-low)/2;   //*****
    if(a[low] > a[high])
        swap(&a[low], &a[high]);
    if(a[mid] > a[high])            //優化："三數取中",平衡遞迴樹
        swap(&a[mid], &a[high]);
    if
 
(a[low] < a[mid])
        swap(&a[low], &a[mid]);     //*****

    int pivotkey = a[low];
    while(low < high)
    {
        while(low < high && a[high] >= pivotkey)
            high--;
        //swap(&a[low], &a[high]);
        a[low] = a[high];   //優化：減少不必要的交換
        while
 
(low < high && a[low] <= pivotkey)
            low++;
        //swap(&a[low], &a[high]);
        a[high] = a[low];   //優化：減少不必要的交換
    }
    a[low] = pivotkey;
    return low;
}

int main()
{
    int i;
    int a[10] = {7, 3, 5, 8, 0, 4, 9, 1, 6, 2};
    for(i = 0; i <10; i++)
        printf("%d ", a[i]);
    printf("\n");
    QuickSort(a, 0, 9);
    for(i = 0; i <10; i++)
        printf("%d ", a[i]);
    printf("\n");

    return 0;
}

void swap(int *a, int *b)
{
    int temp = *a;
    *a = *b;
    *b = temp;
}