Linked List

1 G BHARATHKUMAR, ASSISTANTPROFESSOR,CSEDEPARTMENT
MODULE-3
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.
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.
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 in Memory:
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.
// A linked list node
struct Node
{
int data;
struct Node* next;
};

First Simple Linked List in C Let us create a simple linked list with 3 nodes.
// A simple C program to introduce a linked list
#include <stdio.h>
#include <stdlib.h>
struct Node {
int data;
struct Node* next;
};
// Program to create a simple linked list with 3 nodes
int main()
{
struct Node* head = NULL;
struct Node* second = NULL;
struct Node* third = NULL;
// allocate 3 nodes in the heap
head = (struct Node*)malloc(sizeof(struct Node));
second = (struct Node*)malloc(sizeof(struct Node));
third = (struct Node*)malloc(sizeof(struct Node));
head->data = 1; // assign data in first node
head->next = second; // Link first node with the second node
// assign data to second node
second->data = 2;
// Link second node with the third node
second->next = third;
third->data = 3; // assign data to third node
third->next = NULL;
return 0;
}
Linked List vs Array
Arrays store elements in contiguous memory locations, resulting in easily calculable
addresses for the elements stored and this allows a faster access to an element at a specific
index. Linked lists are less rigid in their storage structure and elements are usually not
stored in contiguous locations, hence they need to be stored with additional tags giving a
reference to the next element. This difference in the data storage scheme decides which
data structure would be more suitable for a given situation.
Data storage scheme of an array

Data storage scheme of a linked list
Major differences are listed below:
 Size: Since data can only be stored in contiguous blocks of memory in an array, its size
cannot be altered at runtime due to risk of overwriting over other data. However in a
linked list, each node points to the next one such that data can exist at scattered (non-
contiguous) addresses; this allows for a dynamic size which can change at runtime.
 Memory allocation: For arrays at compile time and at runtime for linked lists.
 Memory efficiency: For the same number of elements, linked lists use more memory as
a reference to the next node is also stored along with the data. However, size flexibility
in linked lists may make them use less memory overall; this is useful when there is
uncertainty about size or there are large variations in the size of data elements; memory
equivalent to the upper limit on the size has to be allocated (even if not all of it is being
used) while using arrays, whereas linked lists can increase their sizes step-by-step
proportionately to the amount of data.
 Execution time: Any element in an array can be directly accessed with its index;
however in case of a linked list, all the previous elements must be traversed to reach any
element. Also, better cache locality in arrays (due to contiguous memory allocation) can
significantly improve performance. As a result, some operations (such as modifying a
certain element) are faster in arrays, while some other (such as inserting/deleting an
element in the data) are faster in linked lists.
Following are the points in favour of Linked Lists.
(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, and in practical uses, the upper limit is rarely reached.
(2) Inserting a new element in an array of elements is expensive because a room has to be
created for the new elements and to create room existing elements have to be shifted.
For example, suppose 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.
So Linked list provides the following two advantages over arrays
1) Dynamic size
2) Ease of insertion/deletion
Linked lists have following drawbacks:
1) Random access is not allowed. We have to access elements sequentially starting from the

first node. So we cannot do a binary search with linked lists.
2) Extra memory space for a pointer is required with each element of the list.
3) Arrays have better cache locality that can make a pretty big difference in performance.
Inserting a node
Methods to insert a new node in linked list are discussed. A node can be added in three
ways
1) At the front of the linked list
2) After a given node.
3) At the end of the linked list.
1) At the front of the linked list
The new node is always added before the head of the given Linked List. And newly
added node becomes the new head of the Linked List. For example if the given Linked List
is 10->15->20->25 and we add an item 5 at the front, then the Linked List becomes 5->10-
>15->20->25. Let us call the function that adds at the front of the list is push(). The push()
must receive a pointer to the head pointer, because push must change the head pointer to
point to the new node.
We are given pointer to a node, and the new node is inserted after the given node.
3) At the end of the linked list
The new node is always added after the last node of the given Linked List. For
example if the given Linked List is 5->10->15->20->25 and we add an item 30 at the end,
then the Linked List becomes 5->10->15->20->25->30.
Since a Linked List is typically represented by the head of it, we have to traverse the list till

end and then change the next of last node to new node.
Time complexity of append is O(n) where n is the number of nodes in linked list.
Since there is a loop from head to end, the function does O(n) work.
This method can also be optimized to work in O(1) by keeping an extra pointer to tail of
linked list.
Deleting a node
To delete a node from the linked list, we need to do the following steps.
1) Find the previous node of the node to be deleted.
2) Change the next of the previous node.
3) Free memory for the node to be deleted.
Example:
Doubly Linked List

A Doubly Linked List (DLL) contains an extra pointer, typically called previous pointer,
together with next pointer and data which are there in singly linked list.
/* Node of a doubly linked list */
struct Node {
int data;
struct Node* next; // Pointer to next node in DLL
struct Node* prev; // Pointer to previous node in DLL
};
Basic Operations
Following are the important operations supported by a circular list.
 insert − Inserts an element at the start of the list.
 delete − Deletes an element from the start of the list.
 display − Displays the list.
Insertion
A node can be added in four ways
1) At the front of the DLL
3) At the end of the DLL
1) At the front of the DLL
3) At the end of the DLL

Delete a node in a Doubly Linked List
Original Doubly Linked List
1) After the deletion of the head node.
2) After the deletion of the middle node.
3) After the deletion of the last node.
Complexity Analysis:
 Time Complexity: O(1).
Since traversal of the linked list is not required so the time complexity is constant.
 Space Complexity: O(1).
As no extra space is required, so the space complexity is constant.
Circular Linked List
Circular Linked List is a variation of Linked list in which the first element points to the last
element and the last element points to the first element. Both Singly Linked List and Doubly
Linked List can be made into a circular linked list.
Singly Linked List as Circular
In singly linked list, the next pointer of the last node points to the first node.

Doubly Linked List as Circular
In doubly linked list, the next pointer of the last node points to the first node and the
previous pointer of the first node points to the last node making the circular in both
directions.
As per the above illustration, following are the important points to be considered.
 The last link's next points to the first link of the list in both cases of singly as well as
doubly linked list.
 The first link's previous points to the last of the list in case of doubly linked list.
Basic Operations
Following are the important operations supported by a circular list.
 insert − Inserts an element at the start of the list.
 delete − Deletes an element from the start of the list.
 display − Displays the list.
Insertion at the beginning of the list
After Insertion
Insertion at the end of the list

After Insertion
Insertion in between the nodes
After Insertion
Single Linked List
What is Linked List?
When we want to work with an unknown number of data values, we use a linked list data
structure to organize that data. The linked list is a linear data structure that contains a
sequence of elements such that each element links to its next element in the sequence. Each
element in a linked list is called "Node".
What is Single Linked List?
Simply a list is a sequence of data, and the linked list is a sequence of data linked with each
other.
The formal definition of a single linked list is as follows...
Single linked list is a sequence of elements in which every element has link to its next
element in the sequence.

In any single linked list, the individual element is called as "Node". Every "Node" contains
two fields, data field, and the next field. The data field is used to store actual value of the
node and next field is used to store the address of next node in the sequence.
The graphical representation of a node in a single linked list is as follows...
Importent Points to be Remembered
In a single linked list, the address of the first node is always stored in a reference node
known as "front" (Some times it is also known as "head").
Always next part (reference part) of the last node must be NULL.
Example:
Operations on Single Linked List
The following operations are performed on a Single Linked List
 Insertion
 Deletion
 Display
Before we implement actual operations, first we need to set up an empty list. First, perform
the following steps before implementing actual operations.
 Step 1 - Include all the header files which are used in the program.
 Step 2 - Declare all the user defined functions.
 Step 3 - Define a Node structure with two members data and next
 Step 4 - Define a Node pointer 'head' and set it to NULL.
 Step 5 - Implement the main method by displaying operations menu and make
suitable function calls in the main method to perform user selected operation.
Insertion
In a single linked list, the insertion operation can be performed in three ways. They are as
follows...

1. Inserting At Beginning of the list
2. Inserting At End of the list
3. Inserting At Specific location in the list
Inserting At Beginning of the list
We can use the following steps to insert a new node at beginning of the single linked list...
 Step 1 - Create a newNode with given value.
 Step 2 - Check whether list is Empty (head == NULL)
 Step 3 - If it is Empty then, set newNode→next = NULL and head = newNode.
 Step 4 - If it is Not Empty then, set newNode→next = head and head = newNode.
Inserting At End of the list
We can use the following steps to insert a new node at end of the single linked list...
 Step 1 - Create a newNode with given value and newNode → next as NULL.
 Step 2 - Check whether list is Empty (head == NULL).
 Step 3 - If it is Empty then, set head = newNode.
 Step 4 - If it is Not Empty then, define a node pointer temp and initialize with head.
 Step 5 - Keep moving the temp to its next node until it reaches to the last node in the
list (until temp → next is equal to NULL).
 Step 6 - Set temp → next = newNode.
Inserting At Specific location in the list (After a Node)
We can use the following steps to insert a new node after a node in the single linked list...
 Step 3 - If it is Empty then, set newNode → next = NULL and head = newNode.
 Step 5 - Keep moving the temp to its next node until it reaches to the node after
which we want to insert the newNode (until temp1 → data is equal to location, here
location is the node value after which we want to insert the newNode).
 Step 6 - Every time check whether temp is reached to last node or not. If it is reached
to last node then display 'Given node is not found in the list!!! Insertion not
possible!!!' and terminate the function. Otherwise move the temp to next node.
 Step 7 - Finally, Set 'newNode → next = temp → next' and 'temp →
next = newNode'
Deletion
In a single linked list, the deletion operation can be performed in three ways. They are as
follows...
1. Deleting from Beginning of the list
2. Deleting from End of the list
3. Deleting a Specific Node
Deleting from Beginning of the list
We can use the following steps to delete a node from beginning of the single linked list...

 Step 2 - If it is Empty then, display 'List is Empty!!! Deletion is not possible' and
terminate the function.
 Step 3 - If it is Not Empty then, define a Node pointer 'temp' and initialize
with head.
 Step 4 - Check whether list is having only one node (temp → next == NULL)
 Step 5 - If it is TRUE then set head = NULL and delete temp (Setting Empty list
conditions)
 Step 6 - If it is FALSE then set head = temp → next, and delete temp.
Deleting from End of the list
We can use the following steps to delete a node from end of the single linked list...
 Step 3 - If it is Not Empty then, define two Node pointers 'temp1' and 'temp2' and
initialize 'temp1' with head.
 Step 4 - Check whether list has only one Node (temp1 → next == NULL)
 Step 5 - If it is TRUE. Then, set head = NULL and delete temp1. And terminate the
function. (Setting Empty list condition)
 Step 6 - If it is FALSE. Then, set 'temp2 = temp1 ' and move temp1 to its next node.
Repeat the same until it reaches to the last node in the list. (until temp1 →
next == NULL)
 Step 7 - Finally, Set temp2 → next = NULL and delete temp1.
Deleting a Specific Node from the list
We can use the following steps to delete a specific node from the single linked list...
 Step 4 - Keep moving the temp1 until it reaches to the exact node to be deleted or to
the last node. And every time set 'temp2 = temp1' before moving the 'temp1' to its
next node.
 Step 5 - If it is reached to the last node then display 'Given node not found in the
list! Deletion not possible!!!'. And terminate the function.
 Step 6 - If it is reached to the exact node which we want to delete, then check whether
list is having only one node or not
 Step 7 - If list has only one node and that is the node to be deleted, then
set head = NULL and delete temp1 (free(temp1)).
 Step 8 - If list contains multiple nodes, then check whether temp1 is the first node in
the list (temp1 == head).
 Step 9 - If temp1 is the first node then move the head to the next node (head = head
→ next) and delete temp1.
 Step 10 - If temp1 is not first node then check whether it is last node in the list
(temp1 → next == NULL).
 Step 11 - If temp1 is last node then set temp2 → next = NULL and
delete temp1 (free(temp1)).

 Step 12 - If temp1 is not first node and not last node then set temp2 → next = temp1
→ next and delete temp1 (free(temp1)).
Displaying a Single Linked List
We can use the following steps to display the elements of a single linked list...
 Step 2 - If it is Empty then, display 'List is Empty!!!' and terminate the function.
with head.
 Step 4 - Keep displaying temp → data with an arrow (--->) until temp reaches to the
last node
 Step 5 - Finally display temp → data with arrow pointing to NULL (temp → data --
-> NULL).
Implementation of Single Linked List using C Programming
#include<stdio.h>
#include<conio.h>
#include<stdlib.h>
void insertAtBeginning(int);
void insertAtEnd(int);
void insertBetween(int,int,int);
void display();
void removeBeginning();
void removeEnd();
void removeSpecific(int);
struct Node
{
int data;
struct Node *next;
}*head = NULL;
void main()
{
int choice,value,choice1,loc1,loc2;
clrscr();
while(1){

mainMenu: printf("nn****** MENU ******n1. Insertn2. Displayn3. Deleten4. Exitn
Enter your choice: ");
scanf("%d",&choice);
switch(choice)
{
case 1: printf("Enter the value to be insert: ");
scanf("%d",&value);
while(1){
printf("Where you want to insert: n1. At Beginningn2. At Endn3. Betwe
ennEnter your choice: ");
scanf("%d",&choice1);
switch(choice1)
{
case 1: insertAtBeginning(value);
break;
case 2: insertAtEnd(value);
break;
case 3: printf("Enter the two values where you wanto insert: ");
scanf("%d%d",&loc1,&loc2);
insertBetween(value,loc1,loc2);
break;
default: printf("nWrong Input!! Try again!!!nn");
goto mainMenu;
}
goto subMenuEnd;
}
subMenuEnd:
break;
case 2: display();
break;
case 3: printf("How do you want to Delete: n1. From Beginningn2. From Endn3
. SpesificnEnter your choice: ");
switch(choice1)
{

case 1: removeBeginning();
break;
case 2: removeEnd();
break;
case 3: printf("Enter the value which you wanto delete: ");
scanf("%d",&loc2);
removeSpecific(loc2);
break;
default: printf("nWrong Input!! Try again!!!nn");
goto mainMenu;
}
break;
case 4: exit(0);
default: printf("nWrong input!!! Try again!!nn");
}
}
}
void insertAtBeginning(int value)
{
struct Node *newNode;
newNode = (struct Node*)malloc(sizeof(struct Node));
newNode->data = value;
if(head == NULL)
{
newNode->next = NULL;
head = newNode;
}
else
{
newNode->next = head;
head = newNode;
}
printf("nOne node inserted!!!n");

}
void insertAtEnd(int value)
{
if(head == NULL)
head = newNode;
else
{
struct Node *temp = head;
while(temp->next != NULL)
temp = temp->next;
temp->next = newNode;
}
}
void insertBetween(int value, int loc1, int loc2)
{
if(head == NULL)
{
head = newNode;
}
else
{
while(temp->data != loc1 && temp->data != loc2)
temp = temp->next;
newNode->next = temp->next;

temp->next = newNode;
}
}
void removeBeginning()
{
if(head == NULL)
printf("nnList is Empty!!!");
else
{
if(head->next == NULL)
{
head = NULL;
free(temp);
}
else
{
head = temp->next;
free(temp);
printf("nOne node deleted!!!nn");
}
}
}
void removeEnd()
{
if(head == NULL)
{
printf("nList is Empty!!!n");
}
else
{
struct Node *temp1 = head,*temp2;

if(head->next == NULL)
head = NULL;
else
{
while(temp1->next != NULL)
{
temp2 = temp1;
temp1 = temp1->next;
}
temp2->next = NULL;
}
free(temp1);
}
}
void removeSpecific(int delValue)
{
struct Node *temp1 = head, *temp2;
while(temp1->data != delValue)
{
if(temp1 -> next == NULL){
printf("nGiven node not found in the list!!!");
goto functionEnd;
}
temp2 = temp1;
temp1 = temp1 -> next;
}
temp2 -> next = temp1 -> next;
free(temp1);
functionEnd:
}
void display()
{

if(head == NULL)
{
printf("nList is Emptyn");
}
else
{
printf("nnList elements are - n");
while(temp->next != NULL)
{
printf("%d --->",temp->data);
temp = temp->next;
}
printf("%d --->NULL",temp->data);
}
}
Circular Linked List
What is Circular Linked List?
In single linked list, every node points to its next node in the sequence and the last node
points NULL. But in circular linked list, every node points to its next node in the sequence
but the last node points to the first node in the list.

A circular linked list is a sequence of elements in which every element has a link to its next
element in the sequence and the last element has a link to the first element.
That means circular linked list is similar to the single linked list except that the last node
points to the first node in the list
Example
Operations
In a circular linked list, we perform the following operations...
1. Insertion
2. Deletion
3. Display
Before we implement actual operations, first we need to setup empty list. First perform the
following steps before implementing actual operations.
 Step 1 - Include all the header files which are used in the program.
 Step 2 - Declare all the user defined functions.
 Step 3 - Define a Node structure with two members data and next
 Step 4 - Define a Node pointer 'head' and set it to NULL.
 Step 5 - Implement the main method by displaying operations menu and make
suitable function calls in the main method to perform user selected operation.
Insertion
In a circular linked list, the insertion operation can be performed in three ways. They are as
follows...
We can use the following steps to insert a new node at beginning of the circular linked list...
 Step 3 - If it is Empty then, set head = newNode and newNode→next = head .

 Step 4 - If it is Not Empty then, define a Node pointer 'temp' and initialize with
'head'.
 Step 5 - Keep moving the 'temp' to its next node until it reaches to the last node (until
'temp → next == head').
 Step 6 - Set 'newNode → next =head', 'head = newNode' and 'temp → next = head'.
We can use the following steps to insert a new node at end of the circular linked list...
 Step 2 - Check whether list is Empty (head == NULL).
 Step 3 - If it is Empty then, set head = newNode and newNode → next = head.
list (until temp → next == head).
 Step 6 - Set temp → next = newNode and newNode → next = head.
We can use the following steps to insert a new node after a node in the circular linked list...
 Step 3 - If it is Empty then, set head = newNode and newNode → next = head.
 Step 5 - Keep moving the temp to its next node until it reaches to the node after
 Step 6 - Every time check whether temp is reached to the last node or not. If it is
reached to last node then display 'Given node is not found in the list!!! Insertion
not possible!!!' and terminate the function. Otherwise move the temp to next node.
 Step 7 - If temp is reached to the exact node after which we want to insert the
newNode then check whether it is last node (temp → next == head).
 Step 8 - If temp is last node then set temp → next = newNode and newNode →
next = head.
 Step 8 - If temp is not last node then set newNode → next = temp → next and temp
→ next = newNode.
Deletion
In a circular linked list, the deletion operation can be performed in three ways those are as
follows...
We can use the following steps to delete a node from beginning of the circular linked list...

initialize both 'temp1' and 'temp2' with head.
 Step 4 - Check whether list is having only one node (temp1 → next == head)
 Step 5 - If it is TRUE then set head = NULL and delete temp1 (Setting Empty list
conditions)
 Step 6 - If it is FALSE move the temp1 until it reaches to the last node. (until temp1
→ next == head )
 Step 7 - Then set head = temp2 → next, temp1 → next = head and delete temp2.
We can use the following steps to delete a node from end of the circular linked list...
 Step 4 - Check whether list has only one Node (temp1 → next == head)
 Step 5 - If it is TRUE. Then, set head = NULL and delete temp1. And terminate
from the function. (Setting Empty list condition)
 Step 6 - If it is FALSE. Then, set 'temp2 = temp1 ' and move temp1 to its next node.
Repeat the same until temp1 reaches to the last node in the list. (until temp1 →
next == head)
 Step 7 - Set temp2 → next = head and delete temp1.
We can use the following steps to delete a specific node from the circular linked list...
 Step 4 - Keep moving the temp1 until it reaches to the exact node to be deleted or to
the last node. And every time set 'temp2 = temp1' before moving the 'temp1' to its
next node.
 Step 5 - If it is reached to the last node then display 'Given node not found in the
list! Deletion not possible!!!'. And terminate the function.
list is having only one node (temp1 → next == head)
 Step 7 - If list has only one node and that is the node to be deleted then
set head = NULL and delete temp1 (free(temp1)).
 Step 8 - If list contains multiple nodes then check whether temp1 is the first node in
the list (temp1 == head).
 Step 9 - If temp1 is the first node then set temp2 = head and keep moving temp2 to
its next node until temp2 reaches to the last node. Then set head = head →
next, temp2 → next = head and delete temp1.
 Step 10 - If temp1 is not first node then check whether it is last node in the list
(temp1 → next == head).

 Step 1 1- If temp1 is last node then set temp2 → next = head and
delete temp1 (free(temp1)).
 Step 12 - If temp1 is not first node and not last node then set temp2 → next = temp1
→ next and delete temp1 (free(temp1)).
Displaying a circular Linked List
We can use the following steps to display the elements of a circular linked list...
 Step 2 - If it is Empty, then display 'List is Empty!!!' and terminate the function.
with head.
 Step 4 - Keep displaying temp → data with an arrow (--->) until temp reaches to the
last node
 Step 5 - Finally display temp → data with arrow pointing to head → data.
Implementation of Circular Linked List using C Programming
#include<stdio.h>
#include<conio.h>
void insertAtAfter(int,int);
void deleteBeginning();
void deleteEnd();
void deleteSpecific(int);
void display();
struct Node
{
int data;
struct Node *next;
}*head = NULL;
void main()
{
int choice1, choice2, value, location;
clrscr();
while(1)

{
printf("n*********** MENU *************n");
printf("1. Insertn2. Deleten3. Displayn4. ExitnEnter your choice: ");
switch()
{
case 1: printf("Enter the value to be inserted: ");
scanf("%d",&value);
while(1)
{
printf("nSelect from the following Inserting optionsn");
printf("1. At Beginningn2. At Endn3. After a Noden4. CancelnEnter yo
ur choice: ");
switch(choice2)
{
break;
break;
case 3: printf("Enter the location after which you want to insert: ");
scanf("%d",&location);
insertAfter(value,location);
break;
case 4: goto EndSwitch;
default: printf("nPlease select correct Inserting option!!!n");
}
}
case 2: while(1)
{
printf("nSelect from the following Deleting optionsn");
printf("1. At Beginningn2. At Endn3. Specific Noden4. CancelnEnter y
our choice: ");
switch(choice2)

{
case 1: deleteBeginning();
break;
case 2: deleteEnd();
break;
case 3: printf("Enter the Node value to be deleted: ");
deleteSpecic(location);
break;
default: printf("nPlease select correct Deleting option!!!n");
}
}
EndSwitch: break;
case 3: display();
break;
case 4: exit(0);
default: printf("nPlease select correct option!!!");
}
}
}
{
newNode -> data = value;
if(head == NULL)
{
head = newNode;
newNode -> next = head;
}
else
{

while(temp -> next != head)
temp = temp -> next;
head = newNode;
temp -> next = head;
}
printf("nInsertion success!!!");
}
{
if(head == NULL)
{
head = newNode;
}
else
{
temp -> next = newNode;
}
}
void insertAfter(int value, int location)
{

if(head == NULL)
{
head = newNode;
}
else
{
while(temp -> data != location)
{
if(temp -> next == head)
{
printf("Given node is not found in the list!!!");
goto EndFunction;
}
else
{
}
}
newNode -> next = temp -> next;
}
EndFunction:
}
void deleteBeginning()
{
if(head == NULL)
printf("List is Empty!!! Deletion not possible!!!");
else
{
if(temp -> next == head)

{
head = NULL;
free(temp);
}
else{
head = head -> next;
free(temp);
}
printf("nDeletion success!!!");
}
}
void deleteEnd()
{
if(head == NULL)
else
{
struct Node *temp1 = head, temp2;
if(temp1 -> next == head)
{
head = NULL;
free(temp1);
}
else{
while(temp1 -> next != head){
temp2 = temp1;
}
temp2 -> next = head;
free(temp1);
}
}
}

void deleteSpecific(int delValue)
{
if(head == NULL)
else
{
while(temp1 -> data != delValue)
{
{
printf("nGiven node is not found in the list!!!");
goto FuctionEnd;
}
else
{
temp2 = temp1;
}
}
if(temp1 -> next == head){
head = NULL;
free(temp1);
}
else{
if(temp1 == head)
{
temp2 = head;
while(temp2 -> next != head)
head = head -> next;
free(temp1);
}

else
{
{
}
else
{
temp2 -> next = temp1 -> next;
}
free(temp1);
}
}
}
FuctionEnd:
}
void display()
{
if(head == NULL)
printf("nList is Empty!!!");
else
{
printf("nList elements are: n");
{
printf("%d ---> ",temp -> data);
}
printf("%d ---> %d", temp -> data, head -> data);
}
}

Double Linked List
What is Double Linked List?
In a single linked list, every node has a link to its next node in the sequence. So, we can
traverse from one node to another node only in one direction and we can not traverse back.
We can solve this kind of problem by using a double linked list. A double linked list can be
defined as follows...
Double linked list is a sequence of elements in which every element has links to its previous
element and next element in the sequence.
In a double linked list, every node has a link to its previous node and next node. So, we can
traverse forward by using the next field and can traverse backward by using the previous
field. Every node in a double linked list contains three fields and they are shown in the
following figure...
Here, 'link1' field is used to store the address of the previous node in the
sequence, 'link2' field is used to store the address of the next node in the sequence
and 'data' field is used to store the actual value of that node.
Example
Important Points to be Remembered
In double linked list, the first node must be always pointed by head.
Always the previous field of the first node must be NULL.
Always the next field of the last node must be NULL.
Operations on Double Linked List
In a double linked list, we perform the following operations...
1. Insertion
2. Deletion
3. Display

Insertion
In a double linked list, the insertion operation can be performed in three ways as follows...
We can use the following steps to insert a new node at beginning of the double linked list...
 Step 1 - Create a newNode with given value and newNode → previous as NULL.
 Step 3 - If it is Empty then, assign NULL to newNode →
next and newNode to head.
 Step 4 - If it is not Empty then, assign head to newNode →
next and newNode to head.
We can use the following steps to insert a new node at end of the double linked list...
 Step 1 - Create a newNode with given value and newNode → next as NULL.
 Step 3 - If it is Empty, then assign NULL to newNode →
previous and newNode to head.
 Step 4 - If it is not Empty, then, define a node pointer temp and initialize with head.
list (until temp → next is equal to NULL).
 Step 6 - Assign newNode to temp → next and temp to newNode → previous.
We can use the following steps to insert a new node after a node in the double linked list...
 Step 3 - If it is Empty then, assign NULL to both newNode →
previous & newNode → next and set newNode to head.
 Step 4 - If it is not Empty then, define two node pointers temp1 & temp2 and
initialize temp1 with head.
 Step 5 - Keep moving the temp1 to its next node until it reaches to the node after
 Step 6 - Every time check whether temp1 is reached to the last node. If it is reached
to the last node then display 'Given node is not found in the list!!! Insertion not
possible!!!' and terminate the function. Otherwise move the temp1 to next node.
 Step 7 - Assign temp1 → next to temp2, newNode to temp1 →
next, temp1 to newNode → previous, temp2 to newNode →
next and newNode to temp2 → previous.

Deletion
In a double linked list, the deletion operation can be performed in three ways as follows...
We can use the following steps to delete a node from beginning of the double linked list...
 Step 3 - If it is not Empty then, define a Node pointer 'temp' and initialize with head.
 Step 4 - Check whether list is having only one node (temp → previous is equal
to temp → next)
 Step 5 - If it is TRUE, then set head to NULL and delete temp (Setting Empty list
conditions)
 Step 6 - If it is FALSE, then assign temp → next to head, NULL to head →
previous and delete temp.
We can use the following steps to delete a node from end of the double linked list...
 Step 2 - If it is Empty, then display 'List is Empty!!! Deletion is not possible' and
 Step 3 - If it is not Empty then, define a Node pointer 'temp' and initialize with head.
 Step 4 - Check whether list has only one Node (temp → previous and temp →
next both are NULL)
 Step 5 - If it is TRUE, then assign NULL to head and delete temp. And terminate
from the function. (Setting Empty list condition)
 Step 6 - If it is FALSE, then keep moving temp until it reaches to the last node in the
list. (until temp → next is equal to NULL)
 Step 7 - Assign NULL to temp → previous → next and delete temp.
We can use the following steps to delete a specific node from the double linked list...
 Step 3 - If it is not Empty, then define a Node pointer 'temp' and initialize with head.
 Step 4 - Keep moving the temp until it reaches to the exact node to be deleted or to
the last node.
 Step 5 - If it is reached to the last node, then display 'Given node not found in the
list! Deletion not possible!!!' and terminate the fuction.
list is having only one node or not

 Step 7 - If list has only one node and that is the node which is to be deleted then
set head to NULL and delete temp (free(temp)).
 Step 8 - If list contains multiple nodes, then check whether temp is the first node in
the list (temp == head).
 Step 9 - If temp is the first node, then move the head to the next node (head = head
→ next), set head of previous to NULL (head → previous = NULL) and
delete temp.
 Step 10 - If temp is not the first node, then check whether it is the last node in the list
(temp → next == NULL).
 Step 11 - If temp is the last node then set temp of previous of next to NULL (temp
→ previous → next = NULL) and delete temp (free(temp)).
 Step 12 - If temp is not the first node and not the last node, then
set temp of previous of next to temp of next (temp → previous → next = temp →
next), temp of next of previous to temp of previous (temp → next → previous =
temp → previous) and delete temp (free(temp)).
Displaying a Double Linked List
We can use the following steps to display the elements of a double linked list...
 Step 2 - If it is Empty, then display 'List is Empty!!!' and terminate the function.
 Step 3 - If it is not Empty, then define a Node pointer 'temp' and initialize with head.
 Step 4 - Display 'NULL <--- '.
 Step 5 - Keep displaying temp → data with an arrow (<===>) until temp reaches to
the last node
 Step 6 - Finally, display temp → data with arrow pointing to NULL (temp → data -
--> NULL).
Implementation of Double Linked List using C Programming
#include<stdio.h>
#include<conio.h>
void insertAtAfter(int,int);
void deleteBeginning();
void deleteEnd();
void deleteSpecific(int);
void display();
struct Node
{
int data;

struct Node *previous, *next;
}*head = NULL;
void main()
{
int choice1, choice2, value, location;
clrscr();
while(1)
{
printf("n*********** MENU *************n");
printf("1. Insertn2. Deleten3. Displayn4. ExitnEnter your choice: ");
switch()
{
case 1: printf("Enter the value to be inserted: ");
scanf("%d",&value);
while(1)
{
printf("nSelect from the following Inserting optionsn");
printf("1. At Beginningn2. At Endn3. After a Noden4. CancelnEnter yo
ur choice: ");
switch(choice2)
{
break;
break;
case 3: printf("Enter the location after which you want to insert: ");
insertAfter(value,location);
break;
default: printf("nPlease select correct Inserting option!!!n");
}

}
case 2: while(1)
{
printf("nSelect from the following Deleting optionsn");
printf("1. At Beginningn2. At Endn3. Specific Noden4. CancelnEnter y
our choice: ");
switch(choice2)
{
case 1: deleteBeginning();
break;
case 2: deleteEnd();
break;
case 3: printf("Enter the Node value to be deleted: ");
deleteSpecic(location);
break;
default: printf("nPlease select correct Deleting option!!!n");
}
}
EndSwitch: break;
case 3: display();
break;
case 4: exit(0);
default: printf("nPlease select correct option!!!");
}
}
}
{

newNode -> previous = NULL;
if(head == NULL)
{
newNode -> next = NULL;
head = newNode;
}
else
{
head = newNode;
}
}
{
newNode -> next = NULL;
if(head == NULL)
{
newNode -> previous = NULL;
head = newNode;
}
else
{
while(temp -> next != NULL)
newNode -> previous = temp;
}
}

void insertAfter(int value, int location)
{
if(head == NULL)
{
newNode -> previous = newNode -> next = NULL;
head = newNode;
}
else
{
while(temp1 -> data != location)
{
if(temp1 -> next == NULL)
{
printf("Given node is not found in the list!!!");
goto EndFunction;
}
else
{
}
}
temp1 -> next = newNode;
newNode -> previous = temp1;
newNode -> next = temp2;
temp2 -> previous = newNode;
}
EndFunction:
}

void deleteBeginning()
{
if(head == NULL)
else
{
if(temp -> previous == temp -> next)
{
head = NULL;
free(temp);
}
else{
head = temp -> next;
head -> previous = NULL;
free(temp);
}
}
}
void deleteEnd()
{
if(head == NULL)
else
{
if(temp -> previous == temp -> next)
{
head = NULL;
free(temp);
}
else{

temp -> previous -> next = NULL;
free(temp);
}
}
}
void deleteSpecific(int delValue)
{
if(head == NULL)
else
{
while(temp -> data != delValue)
{
if(temp -> next == NULL)
{
printf("nGiven node is not found in the list!!!");
goto FuctionEnd;
}
else
{
}
}
if(temp == head)
{
head = NULL;
free(temp);
}
else
{
temp -> previous -> next = temp -> next;

free(temp);
}
}
FuctionEnd:
}
void display()
{
if(head == NULL)
printf("nList is Empty!!!");
else
{
printf("nList elements are: n");
printf("NULL <--- ");
{
printf("%d <===> ",temp -> data);
}
printf("%d ---> NULL", temp -> data);
}
}
Example:

Linked List

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