How to implement and sort a doubly linked list in PHP

Doubly linked list, also called doubly linked list, is a type of linked list. Each data node has two pointers, pointing to the direct successor and direct predecessor respectively. Therefore, starting from any node in the doubly linked list, you can easily access its predecessor nodes and successor nodes.

<?php
/** 
 * 双向链表实现用户排行榜
 *
 * 仅用于体现思想逻辑，不具备实际参考价值
 * @author 疯狂老司机
 * @date 2016-07-07
 */  
class Rank{  

    /**
     * @var 指向前一个节点的引用
     */
    public $pre = null;

    /**
     * @var 指向后一个节点的引用
     */
    public $next = null;

    /**
     * @var 用户排行id
     */
    public $id;

    /**
     * @var 用户名称
     */
    public $username;
      
    public function __construct($id = &#39;&#39;, $username = &#39;&#39;){
        $this->id = $id;
        $this->username = $username;
    }

    /**
     * 添加成员节点方法
     *
     * @access public
     * @param obj head 初始节点
     * @param obj rank 成员节点
     */
    public static function addRank($head, $rank){
        $cur = $head; // 辅助节点
        $isExist = false; //这是一个标志位

        while($cur->next != null){ 
            if($cur->next->id > $rank->id){
                break;
            }else if($cur->next->id == $rank->id){
                $isExist = true;
                echo&#39;<br/>不能添加相同的id&#39;;  
            }  
            $cur = $cur->next;  
        }  

        if(!$isExist){ 
            if($cur->next != null){  
                $rank->next = $cur->next;  
            }  
            $rank->pre = $cur;  
            if($cur->next != null){  
                $cur->next->pre = $rank;  
            }  
            $cur->next = $rank;  
        }  
    }  

    /**
     * 删除成员节点方法
     *
     * @access public
     * @param obj head 初始节点
     * @param obj rankid 用户排行id
     */
    public static function delRank($head, $rankid){  
        $cur = $head->next;
        $isFind = flase; // 标记位

        while($cur != null){
            if($cur->id == $rankid){
                $isFind = true;
                break;
            }
            $cur = $cur->next;
        }  

        if($isFind){
            if($cur->next != null){
                $cur->next->pre = $cur->pre;
            }
            $cur->pre->next = $cur->next;
            echo &#39;<br/>要删除的成员id是&#39;.$cur->id;
        }else{
            echo&#39;<br/>要删除的成员没有&#39;;
        }
    }

    /**
     * 遍历所有节点并输出显示
     *
     * @access public
     * @param obj head 初始节点
     */
    public static function showRank($head){
        $cur = $head->next; // 不打印空节点
        while($cur->next != null){
            echo&#39;<br/>id=&#39;.$cur->id.&#39;  &#39;.&#39;username=&#39;.$cur->username;
            $cur = $cur->next;
        }
        echo&#39;<br/>id=&#39;.$cur->id.&#39;  &#39;.&#39;username=&#39;.$cur->username;  
    }  
}  

//创建一个初始节点
$head=new Rank();

//创建一个成员
$rank=new Rank(1,&#39;老王&#39;);
Rank::addRank($head,$rank);

$rank=new Rank(2,&#39;小明&#39;);
Rank::addRank($head,$rank);

$rank=new Rank(6,&#39;大熊&#39;);
Rank::addRank($head,$rank);

$rank=new Rank(3,&#39;静香&#39;);
Rank::addRank($head,$rank);

$rank=new Rank(56,&#39;孙二娘&#39;);
Rank::addRank($head,$rank);

echo &#39;<br/>成员排行榜.....&#39;;
Rank::showRank($head);

echo&#39;<br/>&#39;;
echo &#39;<br/>删除后的成员排行榜.....&#39;;
Rank::delRank($head,3);
Rank::showRank($head);

echo&#39;<br/>&#39;;
echo&#39;<br/>下面测试删除最前面的和最后面的成员<br/>&#39;;
echo &#39;<br/>删除后的成员排行榜.....&#39;;
Rank::delRank($head,1);
Rank::showRank($head); 

echo&#39;<br/>&#39;;
echo &#39;<br/>删除后的成员排行榜.....&#39;;
Rank::delRank($head,56);
Rank::showRank($head);
?>

The doubly linked list implemented within PHP will be introduced later. Those who are interested can pay attention to learn more.

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