129. 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 a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    int res = 0;
    public int sumNumbers(TreeNode root) {

        if(root == null) return res;
        bSum(root, 0);
        return res;
    }

    private void bSum(TreeNode root, int value){
        if(root.left == null && root.right == null){
            res += value*10 + root.val;
            return;
        }

        if(root.left != null) bSum(root.left, value*10 + root.val);
        if(root.right != null) bSum(root.right, value*10 + root.val);
    }

}