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.
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]]
方法：DFS
class Solution { private: void find(vector<vector<int>>& res, vector<int>& buffer, int index,int temp_sum, int count_number, int k,int n){ if(count_number > k || temp_sum > n){ return; } if(count_number == k && temp_sum == n){ res.push_back(buffer); return ; } for(int i = index ; i < 10; ++i){ buffer.push_back(i); find(res,buffer,i+1,temp_sum + i,count_number+1,k,n); buffer.pop_back(); } } public: vector<vector<int>> combinationSum3(int k, int n) { vector<vector<int>> res; vector<int> buffer; find(res,buffer,1,0,0,k,n); return res; } };