class Solution {public:    vector
    
     
      > combinationSum(vector
      
       & candidates, int target) {        vector
       
        
         > res;        combinationSumDFS(candidates, target, 0, {}, res);        return res;    }    void combinationSumDFS(vector
         
          & candidates, int target, int start, vector
          
            out, vector
           
            
             >& res) { if (target < 0) return; if (target == 0) {res.push_back(out); return;} for (int i = start; i < candidates.size(); ++i) { out.push_back(candidates[i]); combinationSumDFS(candidates, target - candidates[i], i, out, res); out.pop_back(); } }};