104. Maximum Depth of Binary Tree

题目链接

104. Maximum Depth of Binary Tree

题目分析

返回给定的二叉树有多少层。

思路

每下一级，层树+1，并记录到类属性level中。并判断是否大于已知最深层树。

最终代码

<?php/** * Definition for a binary tree node. * class TreeNode { *     public $val = null; *     public $left = null; *     public $right = null; *     function __construct($value) { $this->val = $value; } * } */class Solution {    public $max = 0;        public $level = 0;            /**                 * @param TreeNode $root                      * @return Integer                           */                               function maxDepth($root) {                                       if($root){                                                   $this->level++;                                                           }                                                                   if($this->level>=$this->max){                                                                               $this->max = $this->level;                                                                                       }                                                                                               if($root->left){                                                                                                           $this->maxDepth($root->left);                                                                                                                   }                                                                                                                           if($root->right){                                                                                                                                       $this->maxDepth($root->right);                                                                                                                                               }                                                                                                                                                       $this->level--;                                                                                                                                                               return $this->max;                                                                                                                                                                   }                                                                                                                                                                   }

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