Leetcode: Sum Root to Leaf Number

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 number123.

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 {    public int sumNumbers(TreeNode root) {// Start typing your Java solution below// DO NOT write main() functionif(root == null)return 0;return calculate(root, 0);}public int calculate(TreeNode root, int temp){temp = temp * 10 + root.val;if(root.left == null && root.right == null)return temp;int left = 0, right = 0;if(root.left != null)left = calculate(root.left, temp);if(root.right != null)right = calculate(root.right, temp);return left + right;}}