1 class Solution  2 { 3 public: 4     vector
     
      
       > combinationSum(vector
       
        & candidates, int target)  5     { 6         sort(candidates.begin(),candidates.end()); 7         vector
        
         
          > res; 8         vector
          
            cur; 9 help(res,cur,candidates,target,0);10 return res;11 }12 13 void help(vector
           
            
             >&res,vector
             
               &cur,vector
              
               &candidates,int target,int index)14 {15 if(target<0)16 return;17 if(target==0)18 {19 res.push_back(cur);20 return;21 } 22 int sz=candidates.size();23 for(int i=index;i
              
             
            
           
          
         
        
       
      
     

这个题，回溯法，很重要，那个pop_back()好好理解