Решение для PHP с кодом Leetcode — d55 429. N-обход порядка на уровне дерева

php
/*
// Definition for a Node.
class Node {
    public $val;
    public $children;

    @param Integer $val 
    @param list $children 
    function __construct($val, $children) {
        $this->val = $val;
        $this->children = $children;
    }
}
*/
class Solution {
    /**
     * @param Node $root
     * @return Integer[][]
     */
    public $level = 0;
    public $values = [];
    function levelOrder($root) {
        if(is_null($root)){
            return $this->values;
        }        
        if(!isset($this->values[$this->level])){
            $this->values[$this->level] = [];
        }
        $this->values[$this->level][] = $root->val;
        foreach($root->children as $child){
            $this->level++;
            $this->levelOrder($child);
            $this->level--;
        }
        
        return $this->values;
    }
}