Method Example of Deleting and Inserting Nodes in Double Linked List by PHP

In this paper, an example is given to describe the method of deleting and inserting nodes in PHP. Share it for your reference, as follows:

Overview:

Two-way linked list is also called double linked list, which is a kind of linked list. There are two pointers in each data node, pointing to direct successor and direct precursor respectively. Therefore, starting from any one node in the bidirectional linked list, it is convenient to access its predecessor node and successor node. 1 We all construct bidirectional circular linked lists.

Implementation code:

<?php 
class node{
  public $prev;
  public $next;
  public $data;
  public function __construct($data,$prev=null,$next=null){
    $this->data=$data;
    $this->prev=$prev;
    $this->next=$next;
  }
}
class doubleLinkList{
  private $head;
  public function __construct()
  {
    $this->head=new node("head",null,null);
  }
  // Insert node 
  public function insertLink($data){
    $p=new node($data,null,null);
    $q=$this->head->next;
    $r=$this->head;
    while($q){
      if($q->data>$data){
        $q->prev->next=$p;
        $p->prev=$q->prev;
        $p->next=$q;
        $q->prev=$p;
      }else{
      $r=$q;$q=$q->next;
      }
    }
    if($q==null){
      $r->next=$p;
      $p->prev=$r;
    }
  }
  // Ab initio output node 
  public function printFromFront(){
    $p=$this->head->next;
    $string="";
    while($p){
    $string.=$string?",":"";
    $string.=$p->data;
    $p=$p->next;
    }
    echo $string."<br>";
  }
  // From tail output node 
  public function printFromEnd(){
    $p=$this->head->next;
    $r=$this->head;
    while($p){
    $r=$p;$p=$p->next;
    }
    $string="";
    while($r){
      $string.=$string?",":"";
      $string.=$r->data;
      $r=$r->prev;
    }
    echo $string."<br>";
  }
  public function delLink($data){
    $p=$this->head->next;
    if(!$p)
    return;
    while($p){
      if($p->data==$data)
      {
        $p->next->prev=$p->prev;
        $p->prev->next=$p->next;
        unset($p);
        return;
      }
      else{
        $p=$p->next;
      }
    }
    if($p==null)
    echo " There is no value of {$data} Node of ";
  }
}
$link=new doubleLinkList();
$link->insertLink(1);
$link->insertLink(2);
$link->insertLink(3);
$link->insertLink(4);
$link->insertLink(5);
$link->delLink(3);
$link->printFromFront();
$link->printFromEnd();
$link->delLink(6);

Run results:

1,2,4,5
5,4,2,1,head
 There is no value of 6 Node of 

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