Leetcode: Subsets II

http://oj.leetcode.com/problems/subsets-ii/

class Solution {
public:
    // First, we sort the input set
    // Second, whenever we have a new element, we count the number of this element
    // Third, we enumerate how many elements we put into the current selection
    vector<vector<int> > res;
    void subsetsWithDupHelper(vector<int> &S, vector<int> current, int pos){
        if(pos==S.size()){
            res.push_back(current);
            return;
        }
        
        int cnt=1;
        while((pos+cnt)<S.size()&&S[pos]==S[pos+cnt]) cnt++;
        for(int i=0;i<=cnt;i++){
            subsetsWithDupHelper(S,current,pos+cnt);
            current.push_back(S[pos]);
        }
    }
    vector<vector<int> > subsetsWithDup(vector<int> &S) {
        res.clear();
        sort(S.begin(),S.end());
        subsetsWithDupHelper(S, vector<int>(), 0);
        return res;
    }
};