leetcode113
看了很多别人的题解，还是感觉没太懂，主要是因为dfs和bfs没彻底会用，还是得找专门的题练练。
得早睡早起呀，假期学习真就靠自律呀。

*** Definition for a binary tree node.* struct TreeNode {*     int val;*     TreeNode *left;*     TreeNode *right;*     TreeNode() : val(0), left(nullptr), right(nullptr) {}*     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}*     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}* };*/
class Solution {
public:vector<vector<int>> pathSum(TreeNode* root, int sum) {if(!root) return {};vector<vector<int>>res;vector<int>nums;dfs(res,nums,sum,root);return res;}void dfs(vector<vector<int>>&res,vector<int>&nums,int sum,TreeNode*root){   nums.push_back(root->val);sum-=root->val;if(!root->left&&!root->right){if(sum==0){res.push_back(nums);}return;}if(root->left){dfs(res,nums,sum,root->left);nums.pop_back();}if(root->right){dfs(res,nums,sum,root->right);nums.pop_back();}}
};