find Max on a PHP Tree

findmax.php

<?php

function createRangeArray(int $max)
{
    if ($max < 0 || $max > PHP_INT_MAX) {
        throw new InvalidArgumentException('You bastard!');
    }

    $result = [];

    for ($i = 0; $i < $max; $i++) {
        $result[$i] = $i;
    }

    return $result;
}

class TreeNode
{
    /**
     * @var int
     */
    public $data;

    public $max;

    /**
     * @var TreeNode[]
     */
    private $children;

    public function __construct(int $data)
    {
        $this->data = $data;
        $this->children = [];
        $this->max = $data;
    }

    public function addChildrenNode(TreeNode &$node)
    {
        array_push($this->children, $node);
        if ($node->max > $this->max) {
            $this->max = $node->max;
        }
    }

    public function addChildren(int $data)
    {
        $node = new TreeNode($data);
        $this->addChildrenNode($node);
        if ($data > $this->max) {
            $this->max = $data;
        }
    }

    public static function findMax(TreeNode $root)
    {
        $max = PHP_INT_MIN;
        $queue = [$root];

        while (!empty($queue)) {
            $node = array_shift($queue);
            if ($node->data > $max) {
                $max = $node->data;
            }
            if (!empty($node->children)) {
                $queue = array_merge($queue, $node->children);
            }
        }
        return $max;
    }


}

$root = new TreeNode(1);
$root->addChildren(2);
$node = new TreeNode(2);
$root->addChildrenNode($node);
$node->addChildren(4);
$node->addChildren(5);
$node->addChildren(8);
$root->addChildren(7);

//var_dump($root);
echo TreeNode::findMax($root);