/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    vector<vector<int>> res;
    vector<int> path;
    int sum;
    vector<vector<int>> findPath(TreeNode* root, int sum) {
        //dfs深搜,dfs中传递两个参数，root，sum,当sum为0时且为叶子，
        //说明当前路径合法，添加到res中，否则
        //如果sum < 0则不合法，if sum > 0则继续递归
        sum = sum;
        dfs(root,sum);
        return res;
    }
    void dfs(TreeNode* root, int sum){
        if(!root) return;
        int x = root->val;
        sum -= x;
        path.push_back(x);
        if(!root->left && !root->right && !sum) res.push_back(path);

        dfs(root->left,sum);
        dfs(root->right,sum);
        path.pop_back();
        sum += x;
    }

};