Given a collection of candidate numbers (C) and a target number (T), find all unique combinations in C where the candidate numbers sums to T.

Each number in C may only be used once in the combination.

Note:

• All numbers (including target) will be positive integers.
• The solution set must not contain duplicate combinations.

 

For example, given candidate set [10, 1, 2, 7, 6, 1, 5] and target 8, 

A solution set is: 

[  [1, 7],  [1, 2, 5],  [2, 6],  [1, 1, 6]]

思路：

典型回溯法，需要注意的就是存在重复情况的处理。

 

 

void combine(vector
     
      
       >& res, vector
       
        & candidates, vector
        
         & cantemp,int begin, int target)     {         if (target < 0) return;                  if ( target == 0)         {             res.push_back(cantemp);             return;         }         for (int i = begin; i < candidates.size();i++)         {             //if (candidates[i]>target)return;             if (i && candidates[i]==candidates[i-1]&& i>begin) continue;//避免重复元素             cantemp.push_back(candidates[i]);             combine(res, candidates, cantemp, i + 1, target - candidates[i]);             cantemp.pop_back();                      }     }     vector
         
          
           > combinationSum2(vector
           
            & candidates, int target) { vector
            
             
              > res; if (candidates.size() == 0)return res; sort(candidates.begin(), candidates.end()); vector
              
                cantemp; combine(res, candidates, cantemp, 0, target); return res; }
              
             
            
           
          
         
        
       
      
     

参考：