LeetCode | 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.

/**
 * Definition for binary tree
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
//注意题目给出的二叉树深度的概念：根节点到“叶子”节点的路径长。
//对{root!=null, left=right=null}的单节点树，其深度为1 [注：也有教材把单节点树的深度定义为0，leetcode定义为1，否则不accepted]

//在求最小深度时，要避免那些只有单个子节点的节点的干扰，因为其为null的子节点会返回0，在取小比较时可能造成其为叶子节点的假象
//而在求最大深度时，单个子节点为空的非叶子节点不会干扰到结果，因为其返回的0在比较大小取大时会被淘汰，从而间接证明其非叶子节点
public class Solution {
    public int maxDepth(TreeNode root) {
        if(root == null) return 0;
        
        int maxleft = maxDepth(root.left);            
        int maxright = maxDepth(root.right);      //递归调用    
        
        int depth = maxleft>=maxright?maxleft:maxright;
        return depth+1;
   }
}