《leetcode-php》有序链表转化为平衡二叉搜索树

给定一个单链表，其中的元素按升序排序，请将它转化成平衡二叉搜索树（BST）

val = $val;
    }
}
class SList{
    public $next = null;
    public $val;
    public function __construct($val) {
        $this->val = $val;
    }
}
function sortedListToBST($head, $end) {
    if ($head == $end) {
        return null;
    }
    $fast = $head;
    $slow = $head;
    while ($fast != $end && $fast->next != $end) {
        $fast = $fast->next->next;
        $slow = $slow->next;
    }
    $node = new Node($slow->val);
    $node->left = sortedListToBST($head, $slow);
    $node->right = sortedListToBST($slow->next, $end);
    return $node;
}
$list1 = new SList(1);
$list2 = new SList(2);
$list3 = new SList(3);
$list4 = new SList(4);
$list5 = new SList(5);
$list1->next = $list2;
$list2->next = $list3;
$list3->next = $list4;
$list4->next = $list5;
$node = sortedListToBST($list1, null);
output($node);
function output($node) {
    print $node->val."\t";
    print "左".$node->left->val."右".$node->right->val."\n";
    if ($node->left != null) {
        output($node->left);
    }
    if ($node->right != null) {
        output($node->right);
    }
    print "\n";
}