#include <iostream>
#include <cstring>
#include <algorithm>
#include <unordered_set>

#include <set>

using namespace std;
int p[3]={1,2,3};//p[n],
unordered_set<int> S;

int main()
{

    for (int i = 1; i < 1<<3; i ++ )//循环次数 1<<n
    {
        int s = 0;
        for (int j = 0; j < 3; j ++ )//j<n
            if (i >> j & 1)//求出所有子集
                s += p[j];
        S.insert(s);
    }

    for (unordered_set<int>::iterator it = S.begin(); it != S.end(); ++it) 
       printf("%d\n", *it);
    return 0;
}

···
输出:
0
6
2
1
3
4
5
···