104 Maximum Depth of Binary Tree

题目链接：https://leetcode.com/problems/maximum-depth-of-binary-tree/

题目

Given a binary tree, find its maximum depth.The maximum depth is the number of nodes along the longest path from the root node down to the farthest leaf node.

解题思路：
1、后序遍历（递归）
2、遍历到叶子节点时，返回1
3、遍历到分支节点时，比较左右子树的高度。返回 较大的子树高度 + 1

注意：
谨慎使用全局变量，会出现莫名其妙的错误，暂时还未查明其中原因。

/** * Definition for a binary tree node. * public class TreeNode { *     int val; *     TreeNode left; *     TreeNode right; *     TreeNode(int x) { val = x; } * } */public class Solution {    public int maxDepth(TreeNode root) {        int resL = 0;        int resR = 0;        if(root == null)            return 0;        if(root.left != null)            resL = maxDepth(root.left);        if(root.right != null)            resR = maxDepth(root.right);        if(root.left == null && root.right == null)            return 1;        int res = resL > resR ? resL : resR;        return res + 1;    }}