LeetCode 216. 组合总和 III（Combination Sum III）

 1 class Solution {
 2 public:
 3     vector<vector<int>> combinationSum3(int k, int n) {
 4         vector<vector<int>> res;
 5         if(k <= 0 || n <= 0) return res;
 6         vector<int> nums, temp;
 7         for(int i = 0; i < 9; i++)
 8             nums.push_back(i + 1);
 9         combine(nums, 0, 0, k, n, temp, res);
10         return res;
11     }
12     void combine(vector<int> nums, int idx, int sum, int k, int n, vector<int> &temp, vector<vector<int>> &res){
13         if(k == 0 && sum == n)
14             res.push_back(temp);
15         else if(sum < n){
16             for(int i = idx; i < 9; i++)
17                 if(sum + nums[i] <= n){
18                     temp.push_back(nums[i]);
19                     combine(nums, i + 1, sum + nums[i], k - 1, n, temp, res);
20                     temp.pop_back();
21                 }
22         }
23     }
24 };