Combination Sum II

class Solution {
public:
    vector<vector<int> > combinationSum2(vector<int> &candidates, int target) {
       vector<int> solution;
       vector< vector<int> > res;
       int sum=0;
       sort(candidates.begin(),candidates.end());
       helper(candidates,solution,res,sum,0,target);
       return res;
    }
    
    void helper(vector<int>& candidates, vector<int>& solution, vector< vector<int> > & res, 
        int& sum, int level, int target)
        {
            if (sum>target)
                return;
            if (sum==target){
                res.push_back(solution);
                return;
            }
            for (int i=level; i<candidates.size();i++){
                sum+=candidates[i];
                solution.push_back(candidates[i]);
                helper(candidates,solution,res,sum,<span style="color:#ff6666;">i+1</span>,target);
                solution.pop_back();
                sum-=candidates[i];
                <span style="color:#ff6666;">while(i<candidates.size()-1 && candidates[i]==candidates[i+1])
                    i++;</span>
            }
        }
};