子集

class Solution {
public:
    vector<vector<int>> subsets(vector<int>& nums) {
        vector<vector<int> > res;
        vector<int> temp;
        res.push_back(temp);
        int i=0;
        for(i; i < nums.size(); i++) {
            int m = nums[i];
            int len = res.size();
            for(int j = 0; j < len; j++) {
                temp = res[j];
                temp.push_back(m);
                res.push_back(temp);
            }
        }
        return res;
    }
};