class Solution {

private:

    vector<vector<int> > ret;

public:

    void generate(vector<int> vet,vector<int> &S,int i){

        if(i==S.size()){

            ret.push_back(vet);

            return;

        }

        generate(vet,S,i+);        //相当于取右子树

        vet.push_back(S[i]);

        generate(vet,S,i+);       //相当于取左子树

    }

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

        ret.clear();

        sort(S.begin(),S.end());

        vector<int> vet;

        generate(vet,S,);

        return ret;

    }

};