使用PHP实现单链表

单链表顾名思义就是一个链式数据结构，它有一个表头，并且除了最后一个节点外，所有节点都有其后继节点。如下图。

首先，我们写出链表节点的类。单链表中的每一个节点，都保存其数据域和后驱指针

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1. //链表节点   
   class node {   
       public $id; //节点id   
       public $name; //节点名称   
       public $next; //下一节点   
        
       public function __construct($id, $name) {   
           $this->id = $id;   
           $this->name = $name;   
           $this->next = null;   
       }   
   }

链表中还有两个特别重要的方法，插入和删除。插入需要找到插入的位置，把前一个元素的next指针指向被插入的节点，并将被插入节点的next指针指向后一个节点，如下图左侧所示。而删除则是把前一个节点的next指针指向后一个节点，并返回被删除元素的数据内容，如下图右侧所示。

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1. //单链表   
   class singelLinkList {   
       private $header; //链表头节点   
        
       //构造方法   
       public function __construct($id = null, $name = null) {   
           $this->header = new node ( $id, $name, null );   
       }   
     
       //获取链表长度   
       public function getLinkLength() {   
           $i = 0;   
           $current = $this->header;   
           while ( $current->next != null ) {   
               $i ++;   
               $current = $current->next;   
           }   
           return $i;   
       }   
     
       //添加节点数据   
       public function addLink($node) {   
           $current = $this->header;   
           while ( $current->next != null ) {   
               if ($current->next->id > $node->id) {   
                   break;   
               }   
               $current = $current->next;   
           }   
           $node->next = $current->next;   
           $current->next = $node;   
       }   
     
       //删除链表节点   
       public function delLink($id) {   
           $current = $this->header;   
           $flag = false;   
           while ( $current->next != null ) {   
               if ($current->next->id == $id) {   
                   $flag = true;   
                   break;   
               }   
               $current = $current->next;   
           }   
           if ($flag) {   
               $current->next = $current->next->next;   
           } else {   
               echo "未找到id=" . $id . "的节点！<br>";   
           }   
       }  
     
       //判断连表是否为空  
       public function isEmpty(){  
               return $this->header == null;  
       }  
     
       //清空链表  
       public function clear(){  
               $this->header = null;  
       }   
     
       //获取链表   
       public function getLinkList() {   
           $current = $this->header;   
           if ($current->next == null) {   
               echo ("链表为空!");   
               return;   
           }   
           while ( $current->next != null ) {   
               echo 'id:' . $current->next->id . '   name:' . $current->next->name . "<br>";   
               if ($current->next->next == null) {   
                   break;   
               }   
               $current = $current->next;   
           }   
       }   
     
       //获取节点名字   
       public function getLinkNameById($id) {   
           $current = $this->header;   
           if ($current->next == null) {   
               echo "链表为空!";   
               return;   
           }   
           while ( $current->next != null ) {   
               if ($current->id == $id) {   
                   break;   
               }   
               $current = $current->next;   
           }   
           return $current->name;   
       }   
     
       //更新节点名称   
       public function updateLink($id, $name) {   
           $current = $this->header;   
           if ($current->next == null) {   
               echo "链表为空!";   
               return;   
           }   
           while ( $current->next != null ) {   
               if ($current->id == $id) {   
                   break;   
               }   
               $current = $current->next;   
           }   
           return $current->name = $name;   
       }   
   }  
   $lists = new singelLinkList ();   
   $lists->addLink ( new node ( 5, 'eeeeee' ) );   
   $lists->addLink ( new node ( 1, 'aaaaaa' ) );   
   $lists->addLink ( new node ( 6, 'ffffff' ) );   
   $lists->addLink ( new node ( 4, 'dddddd' ) );   
   $lists->addLink ( new node ( 3, 'cccccc' ) );   
   $lists->addLink ( new node ( 2, 'bbbbbb' ) );   
   $lists->getLinkList ();   
   echo "<br>-----------删除节点--------------<br>";   
   $lists->delLink ( 5 );   
   $lists->getLinkList ();  
   echo "<br>-----------更新节点名称--------------<br>";   
   $lists->updateLink ( 3, "222222" );   
   $lists->getLinkList ();  
   echo "<br>-----------获取节点名称--------------<br>";   
   echo $lists->getLinkNameById ( 5 );  
   echo "<br>-----------获取链表长度--------------<br>";   
   echo $lists->getLinkLength ();

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