在php中获取二叉树中最后一个左子节点

class TreeNode {
    public $val;
    public $left;
    public $right;

    public function __construct($val = 0, $left = null, $right = null) {
        $this->val = $val;
        $this->left = $left;
        $this->right = $right;
    }
}

function getLastLeftNode($root) {
    if ($root == null) {
        return null;
    }

    $queue = [$root];
    $lastLeftNode = null;

    while (!empty($queue)) {
        $node = array_shift($queue);

        if ($node->left != null) {
            $queue[] = $node->left;
            $lastLeftNode = $node->left;
        }

        if ($node->right != null) {
            $queue[] = $node->right;
        }
    }

    return $lastLeftNode;
}

// 创建一个二叉树
$root = new TreeNode(1);
$root->left = new TreeNode(2);
$root->right = new TreeNode(3);
$root->left->left = new TreeNode(4);
$root->left->right = new TreeNode(5);
$root->right->left = new TreeNode(6);
$root->right->right = new TreeNode(7);

$lastLeftNode = getLastLeftNode($root);
if ($lastLeftNode != null) {
    echo "最后一个左子节点的值为: " . $lastLeftNode->val;
} else {
    echo "二叉树中没有左子节点";
}