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PHP - Delete the first node of the Linked List



In this method, the first node of the 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 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.

Linked List - Delete First Node

The function pop_front is created for this purpose. It is a 3-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;  
  }
}

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

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

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;
    $newNode->next = null; 
    if($this->head == null) {
      $this->head = $newNode;
    } else {
      $temp = new Node();
      $temp = $this->head;
      while($temp->next != null) {
        $temp = $temp->next;
      }
      $temp->next = $newNode;
    }    
  }

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

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

// 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  

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