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.

/**
 * Definition for binary tree
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {    
    int sumnum=0;
    public int sumNumbers(TreeNode root) {          
        if (root==null) {
            return 0;
        }    
                if ((root.left==null)&&(root.right==null)) {
            sumnum=sumnum+root.val;
            return sumnum;
        }
        
        sumNum(root.left, root.val);
        sumNum(root.right, root.val);
        return sumnum;
    }
    
    private    int sumNum(TreeNode root,int numroot){
        if (root==null) {
            return 0;
        }    
        if ((root.left==null)&&(root.right==null)) {
            sumnum=sumnum+numroot*10+root.val;
            return sumnum;
        }
            
            sumNum(root.left, numroot*10+root.val);
            sumNum(root.right, numroot*10+root.val);
            return 0;
        
    }
    }