Subsets

Given a set of distinct integers, S, return all possible subsets.

Note:

• Elements in a subset must be in non-descending order.
• The solution set must not contain duplicate subsets.

For example,
If S = [1,2,3], a solution is:

[
  [3],
  [1],
  [2],
  [1,2,3],
  [1,3],
  [2,3],
  [1,2],
  []
]

 Code:

class Solution {
public:
    void findSub(vector<int> &S, int &n, int level, vector<int> &buf, vector<vector<int>> &res){
        if(buf.size()==n){
            res.push_back(buf);
            return;
        }
        for(int i=level;i<S.size();i++){
            buf.push_back(S[i]);
            findSub(S,n,i+1,buf,res);
            buf.pop_back();
        }
    }
    vector<vector<int> > subsets(vector<int> &S) {
        vector<vector<int>> res;
        vector<int> buf;
        sort(S.begin(),S.end());
        for(int i=0;i<=S.size();i++)
            findSub(S,i,0,buf,res);
        return res;
    }
};