//和77类似的问题，可以放在一起记忆
class Solution {

public:

    vector<vector<int>> subsets(vector<int>& nums) {

        vector<vector<int>> res;

        vector<int> add;

        res.push_back(add);

        for(int i=;i <= nums.size();i++){

            DFS(res,add,nums,i,-);

        }

        return res;

    }

    void DFS(vector<vector<int>>& res,vector<int> &add,vector<int>& nums,int k,int pos){

        if(add.size() == k){

            res.push_back(add);

        }

        else{

            for(int i=pos+;i < nums.size();i++){

                add.push_back(nums[i]);

                DFS(res,add,nums,k,i);

                add.pop_back();

            }

        }

    }

};