[leetcode]Sum Root to Leaf Numbers

 1 /**
 2  * Definition for binary tree
 3  * public class TreeNode {
 4  *     int val;
 5  *     TreeNode left;
 6  *     TreeNode right;
 7  *     TreeNode(int x) { val = x; }
 8  * }
 9  */
10 public class Solution {
11     int res = 0;
12     public int sumNumbers(TreeNode root){
13         if(root == null) return res;
14         dfs(root,0);
15         return res;
16     }
17     private void dfs(TreeNode root,int num){
18         if(root == null) return;
19         if(root.left == null && root.right == null){
20             res += 10 * num + root.val;
21             return;
22         }
23         num = num * 10 + root.val;
24         if(root.left != null){
25             dfs(root.left,num);
26         }
27         if(root.right != null){
28             dfs(root.right,num);
29         }
30     }
31     
32 }