《leetCode-php》删除有序链表中的重复元素为1次

删除有序链表中的重复元素，使链表中的所有元素都只出现一次 

例如： 

给出的链表为1->1->2,返回1->2.

给出的链表为1->1->2->3->3,返回1->2->3.

<?php
class Node {
    public $next = null;
    public $val;
    public function __construct($val) {
        $this->val = $val;
    }
}
function deleteDuplicates($head) {
    $node = $head;
    while ($node != null) {
        if ($node->val == $node->next->val) {
            $node->next = $node->next->next;
        } else {
            $node = $node->next;
        }
    }
    return $head;
}
$node1 = new Node(1);
$node2 = new Node(2);
$node3 = new Node(3);
$node4 = new Node(3);
$node1->next = $node2;
$node2->next = $node3;
$node3->next = $node4;
$ret = deleteDuplicates($node1);
while ($ret != null) {
    print $ret->val . "\n";
    $ret = $ret->next;
}