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.
• Elements in a combination (a₁, a₂, … , a_k) must be in non-descending order. (ie, a₁ ≤ a₂ ≤ … ≤ a_k).
• 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] 

类似与之前的Combination Sum的DFS，有一点需要注意，如何避免重复。如果两个数相同，我们先用前一个数，只有当前一个数用了，这个数才能使用。

例如：1 1。

当我们要使用第二个1时，我们要检查他的前面一个1是否使用了，当未被使用时第二个1就不能使用。

1 class Solution { 2 private: 3     vector
     
      
        > ret; 4     vector
       
         a; 5 public: 6     void solve(int dep, int maxDep, vector
        
          &num, int target) 7     { 8         if (target < 0) 9             return;10             11         if (dep == maxDep)12         {13             if (target == 0)14             {15                 vector
         
           res;16                 for(int i = 0; i < maxDep; i++)17                     for(int j = 0; j < a[i]; j++)18                         res.push_back(num[i]);19                 ret.push_back(res);20             }21             22             return;23         }24         25         for(int i = 0; i <= min(target / num[dep], 1); i++)26         {27             a[dep] = i;28             29             if (i == 1 && dep > 0 && num[dep-1] == num[dep] && a[dep-1] == 0)30                 continue;31                 32             solve(dep + 1, maxDep, num, target - i * num[dep]);33         }34     }35     36     vector
          
           
             > combinationSum2(vector
            
              &num, int target) {37 // Start typing your C/C++ solution below38 // DO NOT write int main() function39 sort(num.begin(), num.end());40 a.resize(num.size());41 ret.clear();42 if (num.size() == 0)43 return ret;44 45 solve(0, num.size(), num, target);46 47 return ret;48 }49 };