LeetCode Sum Root to Leaf Numbers

Given a binary tree containing digits from 0-9 only, each root-to-leaf path could represent a number.

An example is the root-to-leaf path 1->2->3 which represents the number 123.

Find the total sum of all root-to-leaf numbers.

For example,

    1
   / 
  2   3

The root-to-leaf path 1->2 represents the number 12.
The root-to-leaf path 1->3 represents the number 13.

Return the sum = 12 + 13 = 25.

 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 sumnum=0;
12     public int sumNumbers(TreeNode root) {          
13         if (root==null) {
14             return 0;
15         }    
16                 if ((root.left==null)&&(root.right==null)) {
17             sumnum=sumnum+root.val;
18             return sumnum;
19         }
20         
21         sumNum(root.left, root.val);
22         sumNum(root.right, root.val);
23         return sumnum;
24     }
25     
26     private    int sumNum(TreeNode root,int numroot){
27         if (root==null) {
28             return 0;
29         }    
30         if ((root.left==null)&&(root.right==null)) {
31             sumnum=sumnum+numroot*10+root.val;
32             return sumnum;
33         }
34             
35             sumNum(root.left, numroot*10+root.val);
36             sumNum(root.right, numroot*10+root.val);
37             return 0;
38         
39     }
40     }