C# - Delete the first node of the Doubly Linked List

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.

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

public void pop_front() {
  if(this.head != null) {
    
    //1. if head is not null, create a
    //   temp node pointing to head
    Node 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.

using System;

//node structure
class Node {
  public int data;
  public Node next;
  public Node prev;
};

class LinkedList {
  Node head;

  public LinkedList(){
    head = null;
  }
  
  //Add new element at the end of the list
  public void push_back(int newElement) {
    Node newNode = new Node();
    newNode.data = newElement;
    newNode.next = null; 
    newNode.prev = null;
    if(head == null) {
      head = newNode;
    } else {
      Node temp = new Node();
      temp = head;
      while(temp.next != null)
        temp = temp.next;
      temp.next = newNode;
      newNode.prev = temp;
    }    
  }

  //Delete first node of the list
  public void pop_front() {
    if(this.head != null) {
      Node 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 void PrintList() {
    Node temp = new Node();
    temp = this.head;
    if(temp != null) {
      Console.Write("The list contains: ");
      while(temp != null) {
        Console.Write(temp.data + " ");
        temp = temp.next;
      }
      Console.WriteLine();
    } else {
      Console.WriteLine("The list is empty.");
    }
  }     
};

// test the code
class Implementation {  
  static void Main(string[] args) {
    LinkedList 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