39. 组合总和

 1 class Solution 
 2 {
 3     vector<vector<int>> res;
 4     int sum = 0;
 5 public:
 6     void helper(vector<int>& nums, int start,int target, vector<int>& out)
 7     {
 8         if(sum == target)
 9         {
10             res.push_back(out);
11         }
12         
13         if(sum > target) return;
14 
15         for (int i = start; i < nums.size(); ++i)
16         {
17             out.push_back(nums[i]);
18             sum += nums[i];
19             helper(nums, i,target,out);// 数字可以无限制重复被选取，所以是i
20 
21             out.pop_back();
22             sum -= nums[i];
23         }
24     }
25 
26     vector<vector<int>> combinationSum(vector<int>& nums, int target) 
27     {
28         vector<int> out;
29         helper(nums,0,target,out);
30         return res;
31     }
32 };