[LeetCode][Java] 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.

题目大意：

给定一棵二叉树，找到它的最大深度。

最大深度指从根节点到最远的叶子节点的最长路径上的节点数目。

题目分析：

 基础的递归算法应用，看代码就懂了

代码如下：

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

}