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.
https://oj.leetcode.com/problems/maximum-depth-of-binary-tree/
思路：递归求解。
public class Solution { public int maxDepth(TreeNode root) { if (root == null) return 0; return Math.max(maxDepth(root.left), maxDepth(root.right)) + 1; } }
[leetcode] Maximum Depth of Binary Tree,布布扣,bubuko.com
[leetcode] Maximum Depth of Binary Tree
原文：http://www.cnblogs.com/jdflyfly/p/3821332.html
