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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