求教大家一个小算法有关问题

class Node {
	public $data = null;
	public $parent = null;
	public $left = null;
	public $center =null;
	public $right = null;
}

function build_cbtree($a) {
	$root = new Node();
	$root->data = $a[0];
	for ($i = 1; $i < count($a); $i++) {
		$node = new Node();
		$node->data = $a[$i];
		insert_node($root, $node);
	}
	return $root;
}

function insert_node($root, $inode) {
	$queue = array();
	array_unshift($queue, $root);
	while (!empty($queue)) {
		$cnode = array_pop($queue);
		if ($cnode->left == null) {
			$cnode->left = $inode;
			$inode->parent = $cnode;
			return $root;
		} else {
			array_unshift($queue, $cnode->left);                
		}
		if ($cnode->center == null) {
			$cnode->center = $inode;
			$inode->parent = $cnode;
			return $root;
		} else {
			array_unshift($queue, $cnode->center);
		}
		if ($cnode->right == null) {
			$cnode->right = $inode;
			$inode->parent = $cnode;
			return $root;
		} else {
			array_unshift($queue, $cnode->right);
		}
	}
	return $root;
}
//广度优先遍历（先遍历一层，再遍历下一层）
function bf_traverse($root) {
	$queue = array();
	array_unshift($queue, $root);
	while (!empty($queue)) {
		$cnode = array_pop($queue);
		echo $cnode->data . " ";
		if ($cnode->left !== null) array_unshift($queue, $cnode->left);
		if ($cnode->center !== null) array_unshift($queue, $cnode->center);
		if ($cnode->right !== null) array_unshift($queue, $cnode->right);
	}
}

$a = array(1,2,3,4,5,6,7,8);
//先把数组变成三叉树
$root = build_cbtree($a);

echo "
";
print_r($root);
echo "
";
bf_traverse($root);

/*$root数据太多就不打出来了
根据广度优先遍历规则得
1 2 3 4 5 6 7 8
*/

//此时$root就是一个三叉树
//插入9，其实就是重复build_cbtree的方法中for循环的代码
$node1 = new Node();
$node1->data =9;
insert_node($root, $node1);

echo "
";
print_r($root);
echo "
";
bf_traverse($root);
/*
Node Object
(
    [data] => 1
    [parent] => 
    [left] => Node Object
        (
            [data] => 2
            [parent] => Node Object
 *RECURSION*
            [left] => Node Object
                (
                    [data] => 5
                    [parent] => Node Object
 *RECURSION*
                    [left] => 
                    [center] => 
                    [right] => 
                )

            [center] => Node Object
                (
                    [data] => 6
                    [parent] => Node Object
 *RECURSION*
                    [left] =>