最深二叉樹 （Maximum Depth of Binary Tree）

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.

翻譯： 給定一個二叉樹，找到其深度。

此題比較簡單，實現如下:

/**
 * Definition for binary tree
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public int maxDepth(TreeNode root) {
        if(null == root) return 0;
        
        return Math.max(maxDepth(root.left), maxDepth(root.right)) + 1;
    }
}