#include<iostream>

#include<set>

#include<cmath>

#include<ctime>

using namespace std;

#define PI 3.1415926

#define Size 1000

int uniform(set<int> X)//从集合中随机选一个数

{

int m = rand() % X.size();

set<int>::iterator iter = X.begin();

for (int i = 0; i < m; iter++, i++);

return *iter;

}

int SetCount(set<int> X)

{

set<int> S;

int a;

while (S.find(a = uniform(X)) == S.end())//找不到，没有重复出现

{

S.insert(a);

}

return (int)(2 * S.size()*S.size() / PI);

}

int main()

{

set<int> X;

srand((unsigned)time(NULL));

//初始化整数自己 size为1000

for (int i = 0; i < Size; i++) {

X.insert(i);

}

int n;

for (n = 10; n <= 10000; n *= 10) {

int Sum = 0;

for (int i = 0; i < n; i++) {

Sum += SetCount(X);

}

printf("n=%d%t 整数子集的大小 = %d\n", n, (Sum / n));

}

system("pause");

return 0;

}