Data Structures - Doubly Linked List Other Related Topics
Data Structures - Doubly Linked List Other Related Topics

Doubly Linked List - Delete the first node

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 Doubly Linked 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.

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

    //2. move head to next of head
    head = head->next;
    head 

    //3. delete temp node
    free(temp); 

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

void pop_front(struct Node** head_ref) {
  if(*head_ref != NULL) {
    
    //1. if head is not null, create a
    //   temp node pointing to head
    struct Node *temp = *head_ref;
     
    //2. move head to next of head
    *head_ref = (*head_ref)->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(*head_ref != NULL) 
      (*head_ref)->prev = NULL;
  }    
}

def pop_front(self):
  if(self.head != None):
    
    #1. if head is not null, create a
    #   temp node pointing to head
    temp = self.head
    
    #2. move head to next of head
    self.head = self.head.next 
    
    #3. delete temp node
    temp = None 

    #4. If the new head is not null, then
    #   make prev of the new head as null
    if(self.head != None):
      self.head.prev = None

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;
  }
}

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;
  }
}

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.

#include <iostream>
using namespace std;

//node structure
struct Node {
    int data;
    Node* next;
    Node* prev;
};

class LinkedList {
  private:
    Node* head;
  public:
    LinkedList(){
      head = NULL;
    }
 
    //Add new element at the end of the list
    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 = head;
        while(temp->next != NULL)
          temp = temp->next;
        temp->next = newNode;
        newNode->prev = temp;
      }    
    }

    //Delete first node of the list
    void pop_front() {
      if(head != NULL) {
        Node* temp = head;
        head = head->next; 
        free(temp); 
        if(head != NULL)
          head->prev = NULL;
      }
    }

    //display the content of the list
    void PrintList() {
      Node* temp = head;
      if(temp != NULL) {
        cout<<"The list contains: ";
        while(temp != NULL) {
          cout<<temp->data<<" ";
          temp = temp->next;
        }
        cout<<"\n";
      } else {
        cout<<"The list is empty.\n";
      }
    }   
};

// test the code 
int main() {
  LinkedList MyList;

  //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(); 
  
  return 0; 
}

The above code will give the following output: 

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

#include <stdio.h>
#include <stdlib.h>

//node structure
struct Node {
  int data;
  struct Node* next;
  struct Node* prev;
};

//Add new element at the end of the list
void push_back(struct Node** head_ref, int newElement) {  
  struct Node *newNode, *temp;
  newNode = (struct Node*)malloc(sizeof(struct Node)); 
  newNode->data = newElement;  
  newNode->next = NULL;
  newNode->prev = NULL;
  if(*head_ref == NULL) {
    *head_ref = newNode;
  } else {
    temp = *head_ref;
    while(temp->next != NULL) {
      temp = temp->next;
    }    
    temp->next = newNode;
    newNode->prev = temp;
  }
}

//Delete first node of the list
void pop_front(struct Node** head_ref) {
  if(*head_ref != NULL) {
    struct Node *temp = *head_ref;
    *head_ref = (*head_ref)->next;
    temp = NULL; 
    if(*head_ref != NULL) 
      (*head_ref)->prev = NULL;
  }    
}

//display the content of the list
void PrintList(struct Node* head_ref) {
  struct Node* temp = head_ref;
  if(head_ref != NULL) {
    printf("The list contains: ");
    while (temp != NULL) {
      printf("%i ",temp->data);
      temp = temp->next;  
    }
    printf("\n");
  } else {
    printf("The list is empty.\n");
  }   
} 

// test the code 
int main() {
  struct Node* MyList = NULL;

  //Add four elements in the list.
  push_back(&MyList, 10);
  push_back(&MyList, 20);
  push_back(&MyList, 30);
  push_back(&MyList, 40);
  PrintList(MyList);

  //Delete the first node
  pop_front(&MyList);
  PrintList(MyList);

  return 0; 
}

The above code will give the following output: 

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

# node structure
class Node:
  def __init__(self, data):
    self.data = data
    self.next = None
    self.prev = None

#class LinkedList
class LinkedList:
  def __init__(self):
    self.head = None

  #Add new element at the end of the list
  def push_back(self, newElement):
    newNode = Node(newElement)
    if(self.head == None):
      self.head = newNode
      return
    else:
      temp = self.head
      while(temp.next != None):
        temp = temp.next
      temp.next = newNode
      newNode.prev = temp

  #Delete first node of the list
  def pop_front(self):
    if(self.head != None):
      temp = self.head
      self.head = self.head.next 
      temp = None 
      if(self.head != None):
        self.head.prev = None 

  #display the content of the list
  def PrintList(self):
    temp = self.head
    if(temp != None):
      print("The list contains:", end=" ")
      while (temp != None):
        print(temp.data, end=" ")
        temp = temp.next
      print()
    else:
      print("The list is empty.")

# test the code                  
MyList = 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 

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

class LinkedList {
  Node head;

  LinkedList(){
    head = null;
  }

  //Add new element at the end of the list
  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
  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
  void PrintList() {
    Node temp = new Node();
    temp = this.head;
    if(temp != null) {
      System.out.print("The list contains: ");
      while(temp != null) {
        System.out.print(temp.data + " ");
        temp = temp.next;
      }
      System.out.println();
    } else {
      System.out.println("The list is empty.");
    }
  }    
};

// test the code 
public class Implementation {
  public 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 

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 

<?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 "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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