Leetcode PHP题解--D56 637. Average of Levels in Binary Tree

D56 637. Average of Levels in Binary Tree

题目链接

637. Average of Levels in Binary Tree

题目分析

返回每一层的平均值。

思路

和前一篇相似。先保存每一层的值，再逐层计算平均值即可。

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 {
    /**
     * @param TreeNode $root
     * @return Float[]
     */
    public $level = 0;
    public $values = [];
    function averageOfLevels($root) {
        $this->levelValues($root);
        $avg = [];
        foreach($this->values as $values){
            $avg[] = array_sum($values)/count($values);
        }
        return $avg;
    }

    function levelValues($root){
        if(is_null($root)){
            return $this->values;
        }        
        if(!isset($this->values[$this->level])){
            $this->values[$this->level] = [];
        }
        $this->values[$this->level][] = $root->val;
        if($root->left){
            $this->level++;
            $this->averageOfLevels($root->left);
            $this->level--;
        }
        if($root->right){
            $this->level++;
            $this->averageOfLevels($root->right);
            $this->level--;
        }
        return $this->values;
    }
}

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