快排

void quickSort(int* a,int right,int left=0)
{
    int low = left;
    int high = right;

    while(low < high)
    {
        while (low < high && a[low] < a[high])
            high--;
        if (low != high)
        {
            int temp = a[low];
            a[low] = a[high];
            a[high] = temp;
        }
        
        while(low < high && a[low] < a[high])
            low++;
        if (low != high)
        {
            int temp = a[low];
            a[low] = a[high];
            a[high] = temp;
        }
    }

    if (left < low-1)
        quickSort(a,low-1,left);
    if (low+1 < right)
        quickSort(a,right,low+1);
}

例如int a[8] = {4,6,3,5,8,2,1,7};

第一轮:

1 6 3 5 8 2 4 7
1 4 3 5 8 2 6 7
1 2 3 5 8 4 6 7
1 2 3 4 8 5 6 7