subset powerset c++

#include "stdafx.h"
#include <vector>


using namespace std;

// given {1,2,3}, return {{}, {1}, {2}, {3}, {1, 2}, {1, 3}, {2, 3}, {1, 2, 3}}
vector<vector<int>> subsequence(vector<int> arr) {
    if (!arr.size()) {
        vector<int> empty_set;
        vector<vector<int>> retval;
        retval.push_back(empty_set);
        return retval;  // empty set
    }

    int popped = arr[arr.size() - 1];
    arr.pop_back(); // rest

    vector<vector<int>> subsets = subsequence(arr);
    vector<vector<int>> result;
    for (int i = 0; i < subsets.size(); i++) {
        result.push_back(subsets[i]);
        subsets[i].push_back(popped);
        result.push_back(subsets[i]);
    }
    return result;
}

int _tmain(int argc, _TCHAR* argv[])
{
    vector<vector<int>> res = subsequence(vector<int>{1, 2, 3});
    return 0;
}