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× PHP Data Structures - Doubly Linked List Other Related Topics


In this method, the first node of the doubly linked list is deleted. For example - if the given list is 10->20->30->40 and the first node is deleted, the list becomes 20->30->40.

Deleting the first node of the Doubly Linked List is very easy. If the head is not null then create a temp node pointing to head and move head to the next of head. Then delete the temp node. If the new head is not null, make the prev of it as null.

Doubly Linked List - Delete First Node

The function pop_front is created for this purpose. It is a 4-step process.

public function pop_front() {
  if($this->head != null) {
    
    //1. if head is not null, create a
    //   temp node pointing to head
    $temp = $this->head;
    
    //2. move head to next of head
    $this->head = $this->head->next;
    
    //3. delete temp node
    $temp = null;  

    //4. If the new head is not null, then
    //   make prev of the new head as null
    if($this->head != null) 
      $this->head->prev = null; 
  }
}

The below is a complete program that uses above discussed concept of deleting the first node of the doubly linked list.

<?php
//node structure
class Node {
  public $data;
  public $next;
  public $prev;
}

class LinkedList {
  public $head;

  public function __construct(){
    $this->head = null;
  }
  
  //Add new element at the end of the list
  public function push_back($newElement) {
    $newNode = new Node();
    $newNode->data = $newElement;
    $newNode->next = null;
    $newNode->prev = null; 
    if($this->head == null) {
      $this->head = $newNode;
    } else {
      $temp = new Node();
      $temp = $this->head;
      while($temp->next != null) {
        $temp = $temp->next;
      }
      $temp->next = $newNode;
      $newNode->prev = $temp;
    }    
  }

  //Delete first node of the list
  public function pop_front() {
    if($this->head != null) {
      $temp = $this->head;
      $this->head = $this->head->next;
      $temp = null;
      if($this->head != null) 
        $this->head->prev = null;        
    }
  }

  //display the content of the list
  public function PrintList() {
    $temp = new Node();
    $temp = $this->head;
    if($temp != null) {
      echo "\nThe list contains: ";
      while($temp != null) {
        echo $temp->data." ";
        $temp = $temp->next;
      }
    } else {
      echo "\nThe list is empty.";
    }
  }   
};

// test the code  
$MyList = new LinkedList();

//Add four elements in the list.
$MyList->push_back(10);
$MyList->push_back(20);
$MyList->push_back(30);
$MyList->push_back(40);
$MyList->PrintList();

//Delete the first node
$MyList->pop_front();
$MyList->PrintList(); 
?>

The above code will give the following output:

The list contains: 10 20 30 40
The list contains: 20 30 40