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.

Use recursion to do depth first search.

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