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：
递归，JAVA实现如下：
public int maxDepth(TreeNode root) {
if(root==null)
return 0;
return Math.max(maxDepth(root.left), maxDepth(root.right))+1;
}
Java for LeetCode 104 Maximum Depth of Binary Tree
原文：http://www.cnblogs.com/tonyluis/p/4523701.html