How PHP implements a doubly linked list and sorts

A doubly linked list is also called a doubly linked list, which is a list of two pointers in each data node, pointing directly to successive and direct precursors respectively. So, starting from any node in a doubly linked list, it is easy to access its predecessor and successor nodes.

<?php/** * Two-way list implementation User Leaderboard * * Only to embody the thought logic, does not have the actual reference value * @author crazy old driver * @date 2016-07-07 * * * class rank{/** * @var    Reference to the previous node */public $pre = null;    /** * @var A reference to the latter node */public $next = null;    /** * @var user Rank ID */public $id;          /** * @var User name */public $username;        Public function __construct ($id = ', $username = ') {$this->id = $id;    $this->username = $username; }/** * Add member Node method * * @access public * @param obj Head initial node * @param obj Rank member node */public static function Addrank ($head, $rank) {$cur = $head;//secondary node $isExist = false;//This is a flag bit while ($cur-&            Gt;next! = null) {if ($cur->next->id > $rank->id) {break;                }else if ($cur->next->id = = $rank->id) {$isExist = true;              Echo ' <br/> cannot add the same ID ';          } $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 = $rank;     }}/** * Delete member Node method * * @access public * @param obj Head initial node * @param obj rankid user rank ID        */public static function Delrank ($head, $rankid) {$cur = $head->next; $isFind = flase;                Mark bit while ($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 ' <br/> the member ID to remove is '. $cur->id;        }else{Echo ' <br/> the member to remove is not ';}}/** * traverse all nodes and output display * * @access public * @param obj Head initial node */public static function Sho Wrank ($head) {$cur = $head->next;//Do not print empty node while ($cur->next! = null) {echo ' <br/>id= '  . $cur->id. ' '.'            Username= '. $cur->username;        $cur = $cur->next;  } Echo ' <br/>id= '. $cur->id. ' '.'      Username= '. $cur->username; }}//Create an initial node $head=new rank ();//Create a member of $rank=new rank (1, ' Lao Wang '); Rank::addrank ($head, $rank); $rank =new rank (2, ' xiaoming '); Rank::addrank ($head, $rank); $rank =new rank (6, ' Big Bear '); Rank::addrank ($head, $rank); $rank =new rank (3, ' static fragrance '); Rank::addrank ($head, $rank); $rank =new rank (56, ' Erniang '); Rank::addrank ($head, $rank); Echo ' <br/> member leaderboard ...; Rank::showrank ($head); Echo ' <br/> '; Echo ' <br/> deleted member leaderboard ... '; Rank::d Elrank ($head, 3); Rank::showrank ($head); Echo ' <br/> '; Echo ' <br/> the following test deletes the first and last member <br/> '; Echo ' <br/> The member leaderboard after deletion ... '; Rank::d Elrank ($head, 1); Rank::showrank ($head); ECho ' <br/> '; Echo ' <br/> deleted member leaderboard ... '; Rank::d Elrank ($head, 56); Rank::showrank ($head);? >

The

follows a bidirectional list of internal implementations of PHP, which is interesting to follow.