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

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Delete duplicate nodes in the linked list:

1. Define two pointers pre and current

2. The two pointers move backward at the same time. If the current pointer has the same value as the next node, it will move forward alone until there is no equal

3. pre pointer next points directly to the back of the current pointer One, skip all the same ones

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
      }
    }
  }
}

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