LeetCode 216. Combination Sum III

1. 题目描述
   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]]
2. 解题思路
这个题目，大概思路是二叉树深搜，每一个数字只有两种情况放进去还是不放进去。
设置一个数组用来保存当前放进去的结果，再用一个长度来限制一下一组答案的数字个数，剪枝。
3. 实现代码

class Solution {public:    int path[9];    int pathLength=0;    vector<vector<int>> res;    void DFS(int target,int k,int current){        if(target==0&&k==0){            //get result            vector<int> t;            for(int i=0;i<pathLength;++i){                t.push_back(path[i]);            }            res.push_back(t);        }        else if(target<=0||k<=0||current>9){            return;        }        else{            //add this point            path[pathLength++]=current;            DFS(target-current,k-1,current+1);            //no add this point            --pathLength;            DFS(target,k,current+1);        }    }    vector<vector<int>> combinationSum3(int k, int n) {        DFS(n,k,1);        return res;    }};