Combination Sum III

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;    }};