Combination Sum III - LeetCode

Find all possible combinations of k numbers that add up to a number n, given that only numbers from 1 to 9 can be used and each combination should be a unique set of numbers.

Ensure that numbers within the set are sorted in ascending order.

Example 1:

Input: k = 3, n = 7

Output:

 

[[1,2,4]]

 

Example 2:

Input: k = 3, n = 9

Output:

 

[[1,2,6], [1,3,5], [2,3,4]]

思路：这道题和Combination Sum II的思路类似。只不过candidates数组里只有1-9这9个数，且增加了累加次数的限制。

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