How To Create Head Node In Linked List

Like arrays, Linked List is a linear data structure. Unlike arrays, linked list elements are not stored at a contiguous location; the elements are linked using pointers.

linkedlist

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Why Linked List?
Arrays can be used to store linear data of similar types, but arrays have the following limitations.
1) The size of the arrays is fixed: So we must know the upper limit on the number of elements in advance. Also, generally, the allocated memory is equal to the upper limit irrespective of the usage.
2) Inserting a new element in an array of elements is expensive because the room has to be created for the new elements and to create room existing elements have to be shifted.
For example, in a system, if we maintain a sorted list of IDs in an array id[].
id[] = [1000, 1010, 1050, 2000, 2040].
And if we want to insert a new ID 1005, then to maintain the sorted order, we have to move all the elements after 1000 (excluding 1000).
Deletion is also expensive with arrays until unless some special techniques are used. For example, to delete 1010 in id[], everything after 1010 has to be moved.
Advantages over arrays
1) Dynamic size
2) Ease of insertion/deletion
Drawbacks:
1) Random access is not allowed. We have to access elements sequentially starting from the first node. So we cannot do binary search with linked lists efficiently with its default implementation. Read about it here.
2) Extra memory space for a pointer is required with each element of the list.
3) Not cache friendly. Since array elements are contiguous locations, there is locality of reference which is not there in case of linked lists.
Representation:
A linked list is represented by a pointer to the first node of the linked list. The first node is called the head. If the linked list is empty, then the value of the head is NULL.
Each node in a list consists of at least two parts:
1) data
2) Pointer (Or Reference) to the next node
In C, we can represent a node using structures. Below is an example of a linked list node with integer data.
In Java or C#, LinkedList can be represented as a class and a Node as a separate class. The LinkedList class contains a reference of Node class type.

C

struct Node {

int data;

struct Node* next;

};

C++

class Node {

public :

int data;

Node* next;

};

Java

class LinkedList {

Node head;

class Node {

int data;

Node next;

Node( int d) { data = d; }

}

Python

class Node:

def __init__( self , data):

self .data = data

self . next = None

class LinkedList:

def __init__( self ):

self .head = None

C#

class LinkedList {

Node head;

class Node {

int data;

Node next;

Node( int d) { data = d; }

}

Javascript

<script>

var head;

class Node

{

constructor(val) {

this .data = val;

this .next = null ;

}

</script>

First Simple Linked List in C Let us create a simple linked list with 3 nodes.

C++

#include <bits/stdc++.h>

using namespace std;

class Node {

public :

int data;

Node* next;

};

int main()

{

Node* head = NULL;

Node* second = NULL;

Node* third = NULL;

head = new Node();

second = new Node();

third = new Node();

head->data = 1;

head->next = second;

second->data = 2;

second->next = third;

third->data = 3;

third->next = NULL;

return 0;

}

C

#include <stdio.h>

#include <stdlib.h>

struct Node {

int data;

struct Node* next;

};

int main()

{

struct Node* head = NULL;

struct Node* second = NULL;

struct Node* third = NULL;

head = ( struct Node*) malloc ( sizeof ( struct Node));

second = ( struct Node*) malloc ( sizeof ( struct Node));

third = ( struct Node*) malloc ( sizeof ( struct Node));

head->data = 1;

head->next = second;

second->data = 2;

second->next = third;

third->data = 3;

third->next = NULL;

return 0;

}

Java

class LinkedList {

Node head;

static class Node {

int data;

Node next;

Node( int d)

{

data = d;

next = null ;

}

public static void main(String[] args)

{

LinkedList llist = new LinkedList();

llist.head = new Node( 1 );

Node second = new Node( 2 );

Node third = new Node( 3 );

llist.head.next = second;

second.next = third;

}

Python

class Node:

def __init__( self , data):

self .data = data

self . next = None

class LinkedList:

def __init__( self ):

self .head = None

if __name__ = = '__main__' :

llist = LinkedList()

llist.head = Node( 1 )

second = Node( 2 )

third = Node( 3 )

llist.head. next = second;

second. next = third;

C#

using System;

public class LinkedList {

Node head;

public class Node {

public int data;

public Node next;

public Node( int d)

{

data = d;

next = null ;

}

public static void Main(String[] args)

{

LinkedList llist = new LinkedList();

llist.head = new Node(1);

Node second = new Node(2);

Node third = new Node(3);

llist.head.next = second;

second.next = third;

}

Linked List Traversal
In the previous program, we have created a simple linked list with three nodes. Let us traverse the created list and print the data of each node. For traversal, let us write a general-purpose function printList() that prints any given list.

We strongly recommend that you click here and practice it, before moving on to the solution.

C++

#include <bits/stdc++.h>

using namespace std;

class Node {

public :

int data;

Node* next;

};

void printList(Node* n)

{

while (n != NULL) {

cout << n->data << " " ;

n = n->next;

}

int main()

{

Node* head = NULL;

Node* second = NULL;

Node* third = NULL;

head = new Node();

second = new Node();

third = new Node();

head->data = 1;

head->next = second;

second->data = 2;

second->next = third;

third->data = 3;

third->next = NULL;

printList(head);

return 0;

}

C

#include <stdio.h>

#include <stdlib.h>

struct Node {

int data;

struct Node* next;

};

void printList( struct Node* n)

{

while (n != NULL) {

printf ( " %d " , n->data);

n = n->next;

}

int main()

{

struct Node* head = NULL;

struct Node* second = NULL;

struct Node* third = NULL;

head = ( struct Node*) malloc ( sizeof ( struct Node));

second = ( struct Node*) malloc ( sizeof ( struct Node));

third = ( struct Node*) malloc ( sizeof ( struct Node));

head->data = 1;

head->next = second;

second->data = 2;

second->next = third;

third->data = 3;

third->next = NULL;

printList(head);

return 0;

}

Java

class LinkedList {

Node head;

static class Node {

int data;

Node next;

Node( int d)

{

this .data = d;

next = null ;

}

public void printList()

{

Node n = head;

while (n != null ) {

System.out.print(n.data + " " );

n = n.next;

}

public static void main(String[] args)

{

LinkedList llist = new LinkedList();

llist.head = new Node( 1 );

Node second = new Node( 2 );

Node third = new Node( 3 );

llist.head.next = second;

second.next = third;

llist.printList();

}

Python3

class Node:

def __init__( self , data):

self .data = data

self . next = None

class LinkedList:

def __init__( self ):

self .head = None

def printList( self ):

temp = self .head

while (temp):

print (temp.data)

temp = temp. next

if __name__ = = '__main__' :

llist = LinkedList()

llist.head = Node( 1 )

second = Node( 2 )

third = Node( 3 )

llist.head. next = second;

second. next = third;

llist.printList()

C#

using System;

public class LinkedList {

Node head;

public class Node {

public int data;

public Node next;

public Node( int d)

{

data = d;

next = null ;

}

public void printList()

{

Node n = head;

while (n != null ) {

Console.Write(n.data + " " );

n = n.next;

}

public static void Main(String[] args)

{

LinkedList llist = new LinkedList();

llist.head = new Node(1);

Node second = new Node(2);

Node third = new Node(3);

llist.head.next = second;

second.next = third;

llist.printList();

}

Javascript

<script>

var head;

class Node {

constructor(val) {

this .data = val;

this .next = null ;

}

function printList()

{

var n = head;

while (n != null ) {

document.write(n.data + " " );

n = n.next;

}

var head = new Node(1);

var second = new Node(2);

var third = new Node(3);

head.next = second;

second.next = third;

printList();

</script>

Output:

          1  2  3

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