快速排序的随机化版本

#include<iostream>
#include<ctime>
using namespace std;
int Partition(int *A, int p, int r)
{
    int x = A[r];
    int i = p - 1;
    for (int j = p; j < r; j++)
    {
        if (A[j] < x)
        {
            i++;
            swap(A[i],A[j]);
        }
    }
    swap(A[i+1],A[r]);
    return (i+1);
}
int Random(int M, int N)
{
    return (int)((double)rand() / (double)RAND_MAX*(N - M + 1) + M);
}
int Random_Partition(int *A, int p, int r)
{
    int i = Random(p,r);
    swap(A[r],A[i]);
    return Partition(A, p, r);
}
void QuickSort(int *A, int p, int r)
{
    if (p < r)
    {
        int q = Random_Partition(A, p, r);
        QuickSort(A, p, q - 1);
        QuickSort(A,q+1,r);
    }
}
int main()
{
    int A[] = {2,8,7,1,3,5,6,4};
    int N = sizeof A / sizeof A[0];
    srand((int)time(0));//必须放在调用前，不可放到产生随机数的函数中
    QuickSort(A, 0, N-1);
    for (int i = 0; i < N; i++)
        cout << A[i] << "  ";
    cout << "
";
    return 0;

}