class Node{
      public $data=null;
      public $next = null;
      public function __construct($data=null){
         $this->data = $data;
      }
   }

   class LinkdList{
      public $header=null;
      public function __construct($data=null){
         $this->header= new Node();
      }
      //插入
      public function insert($data){
         $current = $this->header;
         $newNode = new Node($data);

         while($current->next){
            if($current->next != $this->header){
               $current = $current->next;
            }else{
               break;   
            }
         }
         $current->next = $newNode;
         $newNode->next = $this->header;
      }
      //查找所在位置
      public function find($data){
         $current = $this->header->next;
         $index=1;
         while($current){
            if($current->data == $data){
               break;
            }else{
               $index++;
               $current = $current->next;
            }
         }
         return $index;
      }

      //固定位置修改
      public function update($data,$num){
         $current = $this->header->next;
         $index=1;
         while($index < $num ){
            $current = $current->next;
            $index++;
         }
         $current->data=$data;
      }
      //添加
      public function add($data,$num){
         $current = $this->header->next;
         $index=1;
         $newNode = new Node($data);
         while($index < $num){
            $prev = $current;
            $current=$current->next;
            $index++;
         }
         $prev->next = $newNode;
         $newNode->next = $current;
      }

      //删除
      public function del($num){
         $current = $this->header->next;
         $index = 1;
         while($index < $num){
            $prev = $current;
            $current = $current->next;
            $index++;
         }
         $prev->next = $current->next;
      }

      //遍历
      public function listLink(){
            $current=$first = $this->header;
            while($current){
               $current = $current->next;
               if($current == $first){
                  break;
               }
               echo $current->data;
               echo "\r\n";
            }
        }
   }

   //$arr=[10,304,4,5,1,30];
   $arr=[10,304,4,5,1,30,38];
    $obj  = new LinkdList();
    foreach ($arr as $key => $value) {
        $obj->insert($value);
    }
    //$obj->update(100,2);
    //$obj->add(90,4);
   //echo  $obj->find(5);
   $obj->del(4);
   $obj->listLink();