[Leetcode]Combination Sum III

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Combination Sum III My Submissions Question
Total Accepted: 17981 Total Submissions: 56703 Difficulty: Medium
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]]
Credits:
Special thanks to @mithmatt for adding this problem and creating all test cases.

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class Solution {public:    vector<vector<int>> combinationSum3(int k, int n) {        vector<vector<int> >    res;        vector<int> tem;        dfs(k,n,1,tem,res);        return res;    }private:    void dfs(int k,int n,int i,vector<int>& tem,vector<vector<int> >& res){        if(k == 0 && n == 0){            res.push_back(tem);            //tem.clear();//开始时候写了这句怎么改怎么错，原先想的是把这个tem放进结果之后，tem就要清空用来存下一个可能的序列.事实上，所谓的删除操作直接由下面的tem.pop_back()完成了。这里很值得我注意！            return;        }        if(k == 0 && n > 0) return;        for(int j = i;j <= 9;++j){            tem.push_back(j);            dfs(k - 1,n - j,j + 1,tem,res);            tem.pop_back();        }        return;    }};