// 既然不能重复利用，就在递归中选择下一个数，不能重复的话，就用set class Solution {public:    vector
     
      
       > combinationSum2(vector
       
        & candidates, int target) {        set
        
         
          > res;        sort(candidates.begin(),candidates.end());        vector
          
            add; DFS(candidates,target,0,add,res); return vector
           
            
             >(res.begin(),res.end()); } void DFS(vector
             
              & candidates, int target,int start,vector
              
               & add,set
               
                
                 >& res){ if(target < 0)return; else if(target == 0){res.insert(add);} else{ for(int i=start;i < candidates.size();i++){ add.push_back(candidates[i]); DFS(candidates,target-candidates[i],i+1,add,res); add.pop_back(); } } }};