定义链表 
  class ListNode { 
     public $val = NULL; 
     public $next = NULL; 
   function __construct($val = 0, $next = null) {
           $this->val = $val;
           $this->next = $next;
      }
  }
   
   

  class LinkList { 
     public $next=null;
     public function insert($val = NULL) { 
        $newNode = new ListNode($val); 
        if ($this->next === NULL) {           
            $this->next = $newNode;             
        } else { 
            $currentNode = $this->next; 
            while ($currentNode->next !== NULL) { 
                $currentNode = $currentNode->next; 
         } 
            $currentNode->next = $newNode; 
        } 
    }
   public function insert_arr($arr = array() ) { 
       foreach($arr as $val){
          $this->insert($val);  
       }
 
     }
  public function display() { 
  echo "当前链表的是: <br/>"; 
        $currentNode = $this->next; 
        while ($currentNode !== NULL) { 
            echo $currentNode->val . "\n"; 
            $currentNode = $currentNode->next; 
        } 
    } 
  }