How to find the entry node of a ring with a ring linked list in PHP (code example)

slow fast
while fast!=null && fast->next!=null
    slow=slow->next
    fast=fast->next->next
    if slow==fast
        fast=head
        while slow!=fast
            slow=slow->next
            fast=fast->next
        if slow==fast
            return slow
return null

<?php
class Node{
        public $data;
        public $next;
        public function __construct($data=""){
                $this->data=$data;
        }   
}
//构造一个带环的链表
$linkList=new Node();
$linkList->next=null;
$temp=$linkList;

$node1=new Node("111");
$temp->next=$node1;
$temp=$node1;

$node2=new Node("222");
$temp->next=$node2;
$temp=$node2;

$node3=new Node("333");
$temp->next=$node3;
$temp=$node3;

$node4=new Node("444");
$temp->next=$node4;
$node4->next=$node2;//尾结点指向第二个结点

function EntryNodeOfLoop($pHead){
        $slow=$pHead;
        $fast=$pHead;
        while($fast!=null && $fast->next!=null){
                $slow=$slow->next;//慢指针走一步
                $fast=$fast->next->next;//快指针走两步
                //快慢指针环内相遇
                if($slow==$fast){
                        //快指针回到头结点
                        $fast=$pHead;
                        //同一速度再同时走
                        while($slow!=$fast){
                                $slow=$slow->next;
                                $fast=$fast->next;
                        }   
                        //两个相遇的点一定是环的入口
                        if($slow==$fast){
                                return $fast;
                        }   
                }   
        }   
}
var_dump($linkList);
$result=EntryNodeOfLoop($linkList);
var_dump($result);

object(Node)#1 (2) {
  ["data"]=>  string(0) ""
  ["next"]=>  object(Node)#2 (2) {
    ["data"]=>    string(3) "111"
    ["next"]=>    object(Node)#3 (2) {
      ["data"]=>      string(3) "222"
      ["next"]=>      object(Node)#4 (2) {
        ["data"]=>        string(3) "333"
        ["next"]=>        object(Node)#5 (2) {
          ["data"]=>          string(3) "444"
          ["next"]=>
          *RECURSION*
        }
      }
    }
  }
}object(Node)#3 (2) {
  ["data"]=>  string(3) "222"
  ["next"]=>  object(Node)#4 (2) {
    ["data"]=>    string(3) "333"
    ["next"]=>    object(Node)#5 (2) {
      ["data"]=>      string(3) "444"
      ["next"]=>
      *RECURSION*
    }
  }
}