php线性表小例子

<?php/** 类名：LNode* 功能：线性表的链式存储实现* @author xxy*/ini_set('display_errors',1);error_reporting(E_ALL);class Node {    public  $key = null;    public  $data = null;     //存储数据元素    public  $next = null;     //存储下一个数据元素的地址}class LinkList{   private $head = null;   private $end = null;   public function insert($key, $data){        $node = new Node();        $node->key = $key;        $node->data = $data;        if($this->end==null){          $this->end = $node;                  }else{          $this->end->next =  $node;          $this->end = $node;        }       if ($this->head == null){            $this->head = $node;       }       return $node;    }    public function del_node($key){      $node = $this->head;      //echo $node; exit;      $pre_node = null;            while ( $node != null ){                    if ($node->key == $key){              if($pre_node == null ){                      $this->head = $node->next;                      //$this->end;                      if ($this->end == $node){                          $this->end = null;                      }              }else{                $pre_node->next = $node->next;              }                           break;          }          $pre_node = $node;          $node = $node->next;      }        }  public function select($key){       $node = $this->head;      //echo $node; exit;       $pre_node = null;      while ( $node != null ){                    if ($node->key == $key){                      $node_data = $node->head->data;              break;          }else{          $pre_node = $node;          $node = $node->next;          }      }      return  $node_data;  }}function test_link_insert_end(){    $link = new LinkList();    $info = array();    for($i=1;$i<5;$i++) {      $link->insert($i, $i);                   }    return $link;}$link = test_link_insert_end();print_r($link);$s = $link->select(2);$s = $link->del_node(3);print_r($link);print_r($s);?>