PHP 函数中如何使用递归来实现广度优先搜索？

function bfs($node) {
    // 声明一个队列
    $queue = new SplQueue();

    // 将传入的节点放入队列
    $queue->enqueue($node);

    // 重复步骤，直到队列为空
    while (!$queue->isEmpty()) {
        
        // 从队列中取出一个节点
        $node = $queue->dequeue();

        // 对节点进行处理

        // 将节点的所有邻居放入队列
        foreach ($node->neighbors as $neighbor) {
            $queue->enqueue($neighbor);
        }
    }
}

class Node {
    public $value;
    public $children = [];
}

$tree = [
    new Node(['value' => 'root', 'children' => [
        new Node(['value' => 'child1', 'children' => [
            new Node(['value' => 'grandchild1']),
            new Node(['value' => 'grandchild2'])
        ])),
        new Node(['value' => 'child2', 'children' => [
            new Node(['value' => 'grandchild3']),
            new Node(['value' => 'grandchild4'])
        ]])
    ]])
];

// 从根节点开始 BFS
bfs($tree[0]);