Leetcode -- Path Sum II

Very simple recursion question

 /**  
  * Definition for binary tree  
  * 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;  
     if(root == NULL) {  
       return result;    
     }  
     if(root->left == NULL && root->right == NULL) {  
       if(sum == root->val) {  
         vector<int> temp{root->val};  
         result.emplace_back(temp);  
         return result;  
       }  
     }  
     if(root->left != NULL) {  
       auto ret = pathSum(root->left, sum - root->val);  
       for(vector<int>& v: ret) {  
         vector<int> newV{root->val};  
         for(int i : v) {  
           newV.emplace_back(i);  
         }  
         result.emplace_back(newV);  
       }  
     }  
     if(root->right != NULL) {  
       auto ret = pathSum(root->right, sum - root->val);  
       for(vector<int>& v: ret) {  
         vector<int> newV{root->val};  
         for(int i : v) {  
           newV.emplace_back(i);  
         }  
         result.emplace_back(newV);  
       }  
     }  
     return result;  
   }  
 };