# Linked List

A linked list is a linear data structure, in which the elements are stored in the form of a node. Each node contains two sub-elements. A data part that stores the value of the element and next part that stores the pointer to the next node as shown in the below image:

The first node also known as HEAD is always used as a reference to traverse the list. The last node points to NULL. Linked list can be visualized as a chain of nodes, where every node points to the next node.

## Types of Linked List

The types of linked list are mentioned below:

**Singly Linked List**: can be traversed only in forward direction.**Doubly Linked List**: can be traversed in forward and backward directions.**Circular Singly Linked List**: Last element contains link to the first element as next.**Circular Doubly Linked List**: Last element contains link to the first element as next and the first element contains link of the last element as previous.

## Implementation of Singly Linked List

### Representation:

In C, a node can be created using structure. In C++, singly linked list can be created using a class and a Node using structures. The LinkedList class contains Node as class member.

In Java, Python, C# and PHP, singly linked list can be represented as a class and a Node as a separate class. The LinkedList class contains a reference of Node class type.

//node structure struct Node { int data; Node* next; }; class LinkedList { public: Node* head; public: //constructor to create an empty LinkedList LinkedList(){ head = NULL; } };

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

# node structure class Node: #constructor to create a new node def __init__(self, data): self.data = data self.next = None #class Linked List class LinkedList: #constructor to create an empty LinkedList def __init__(self): self.head = None

//node structure class Node { int data; Node next; }; class LinkedList { Node head; //constructor to create an empty LinkedList LinkedList(){ head = null; } };

//node structure class Node { public int data; public Node next; }; class LinkedList { public Node head; //constructor to create an empty LinkedList public LinkedList(){ head = null; } };

//node structure class Node { public $data; public $next; } class LinkedList { public $head; //constructor to create an empty LinkedList public function __construct(){ $this->head = null; } };

### Create a Singly Linked List

Let us create a simple singly linked list which contains three data nodes.

#include <iostream> using namespace std; //node structure struct Node { int data; Node* next; }; class LinkedList { public: Node* head; public: //constructor to create an empty LinkedList LinkedList(){ head = NULL; } }; // test the code int main() { //create an empty LinkedList LinkedList MyList; //Add first node. Node* first = new Node(); first->data = 10; first->next = NULL; //linking with head node MyList.head = first; //Add second node. Node* second = new Node(); second->data = 20; second->next = NULL; //linking with first node first->next = second; //Add third node. Node* third = new Node(); third->data = 30; third->next = NULL; //linking with second node second->next = third; return 0; }

#include <stdio.h> #include <stdlib.h> //node structure struct Node { int data; struct Node* next; }; // test the code int main() { //create the head node with name MyList struct Node* MyList = NULL; //Add first node. struct Node* first; //allocate second node in the heap first = (struct Node*)malloc(sizeof(struct Node)); first->data = 10; first->next = NULL; //linking with head node MyList = first; //Add second node. struct Node* second; //allocate second node in the heap second = (struct Node*)malloc(sizeof(struct Node)); second->data = 20; second->next = NULL; //linking with first node first->next = second; //Add third node. struct Node* third; //allocate third node in the heap third = (struct Node*)malloc(sizeof(struct Node)); third->data = 30; third->next = NULL; //linking with second node second->next = third; return 0; }

# node structure class Node: #constructor to create a new node def __init__(self, data): self.data = data self.next = None #class Linked List class LinkedList: #constructor to create an empty LinkedList def __init__(self): self.head = None # test the code # create an empty LinkedList MyList = LinkedList() #Add first node. first = Node(10) #linking with head node MyList.head = first #Add second node. second = Node(20) #linking with first node first.next = second #Add third node. third = Node(30) #linking with second node second.next = third

//node structure class Node { int data; Node next; }; class LinkedList { Node head; //constructor to create an empty LinkedList LinkedList(){ head = null; } }; // test the code public class Implementation { public static void main(String[] args) { //create an empty LinkedList LinkedList MyList = new LinkedList(); //Add first node. Node first = new Node(); first.data = 10; first.next = null; //linking with head node MyList.head = first; //Add second node. Node second = new Node(); second.data = 20; second.next = null; //linking with first node first.next = second; //Add third node. Node third = new Node(); third.data = 30; third.next = null; //linking with second node second.next = third; } }

using System; //node structure class Node { public int data; public Node next; }; class LinkedList { public Node head; //constructor to create an empty LinkedList public LinkedList(){ head = null; } }; // test the code class Implementation { static void Main(string[] args) { //create an empty LinkedList LinkedList MyList = new LinkedList(); //Add first node. Node first = new Node(); first.data = 10; first.next = null; //linking with head node MyList.head = first; //Add second node. Node second = new Node(); second.data = 20; second.next = null; //linking with first node first.next = second; //Add third node. Node third = new Node(); third.data = 30; third.next = null; //linking with second node second.next = third; } }

<?php //node structure class Node { public $data; public $next; } class LinkedList { public $head; //constructor to create an empty LinkedList public function __construct(){ $this->head = null; } }; // test the code //create an empty LinkedList $MyList = new LinkedList(); //Add first node. $first = new Node(); $first->data = 10; $first->next = null; //linking with head node $MyList->head = $first; //Add second node. $second = new Node(); $second->data = 20; $second->next = null; //linking with first node $first->next = $second; //Add third node. $third = new Node(); $third->data = 30; $third->next = null; //linking with second node $second->next = $third; ?>