How to delete duplicate nodes in a linked list in php? (code example)

pre=linkList
current=linkList
while current!=null
    if current->data==current->next->data
        value=current->data
        while value==current->next->data
            current=current->next
        pre->next=current->next
    pre=pre->next
    current=current->next
return linkList

<?php
class Node{
        public $data;
        public $next;
        public function __construct($data=""){
                $this->data=$data;
        }   
}
//构造一个带重复的链表
$linkList=new Node();
$linkList->next=null;
$temp=$linkList;
$node1=new Node(2);
$temp->next=$node1;
$temp=$node1;
$node2=new Node(2);
$temp->next=$node2;
$temp=$node2;
$node3=new Node(3);
$temp->next=$node3;
$temp=$node3;
$node4=new Node(3);
$temp->next=$node4;
$temp=$node4;
$node5=new Node(4);
$temp->next=$node5;
$node5->next=null;
function deleteDuplication($pHead){
        $pre=$pHead->next;//当前都指向第一个结点
        $current=$pHead->next;//当前结点是第一个结点
        while($current!=null){
                //如果当前结点值和当前结点的下一个结点值相同
                if($current->next!=null && $current->data==$current->next->data){
                        //保存当前结点值
                        $val=$current->data;
                        //当前结点往后移直到和下一个结点值不相等
                        while($current->next!=null && $val==$current->next->data){
                                $current=$current->next;
                        }   
                        //前一个指针next直接指向当前结点的next
                        $pre->next=$current->next;
                }   
                //两个指针同时后移
                $pre=$pre->next;
                $current=$current->next;
        }
        return $pHead;
}
var_dump($linkList);
$result=deleteDuplication($linkList);
var_dump($result);

object(Node)#1 (2) {
  ["data"]=>
  string(0) ""
  ["next"]=>
  object(Node)#2 (2) {
    ["data"]=>
    int(2)
    ["next"]=>
    object(Node)#3 (2) {
      ["data"]=>
      int(2)
      ["next"]=>
      object(Node)#4 (2) {
        ["data"]=>
        int(3)
        ["next"]=>
        object(Node)#5 (2) {
          ["data"]=>
          int(3)
          ["next"]=>
          object(Node)#6 (2) {
            ["data"]=>
            int(4)
            ["next"]=>
            NULL
          }
        }
      }
    }
  }
}
object(Node)#1 (2) {
  ["data"]=>
  string(0) ""
  ["next"]=>
  object(Node)#2 (2) {
    ["data"]=>
    int(2)
    ["next"]=>
    object(Node)#4 (2) {
      ["data"]=>
      int(3)
      ["next"]=>
      object(Node)#6 (2) {
        ["data"]=>
        int(4)
        ["next"]=>
        NULL
      }
    }
  }
}