leetcode 47: 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],
  []
]

class Solution {
public:
    vector<vector<int> > subsets(vector<int> &S) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        vector<vector<int> > res;
        vector<int> temp;
        res.push_back( temp );
        
        sort( S.begin(), S.end() );
        
        subsetsRec( S, res, temp, 0);
        return res;
    }
    
private:
    void subsetsRec(vector<int> &s, vector<vector<int> > & res, vector<int> & temp , int level) {
        int len = s.size();
        if( level > len ) {
            return;
        }
        
        for( int i=level; i< len; i++) {
            temp.push_back( s[i] );
            res.push_back( temp );
            subsetsRec( s, res, temp, i + 1);
            temp.pop_back();
        }
        return;
    }
};