113.txt

/**
 * 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>> pathSum(TreeNode* root, int sum) {
        vector<vector<int>> result;
        vector<int> path;
        path_sum(root,path,result,sum);
        return result;

    }
private:
        void path_sum(TreeNode* root,vector<int>& path,vector<vector<int>>& result,int gap){
            if(root == nullptr) return;
            else
                 path.push_back(root -> val);
                if(root -> left ==nullptr && root ->right == nullptr){
                    if (gap == root -> val) result.push_back(path);
                }
                int newgap = gap - root->val;
                path_sum(root ->left, path, result,newgap);
                path_sum(root ->right, path, result,newgap);
                path.pop_back();  //回溯







        }
    


        
    
};