Doubly linked lists allow navigation in both directions by linking each node to both the next and previous nodes. Each node contains data and pointers to the next and previous nodes. Operations like insertion and deletion are more complex than with singly linked lists since both next and previous pointers must be updated. However, elements can be easily accessed from either direction. Basic operations on doubly linked lists include insertion and deletion at the beginning, end, or at a specified position in the list by adjusting the relevant next and previous pointers.

1. Mrs.G.Chandraprabha,M.Sc.,M.Phil.,
Assistant Professor,
Department of Information Technology,
V.V.Vanniaperumal College for Women,
Virudhunagar.

2. Doubly Linked List is a variation of Linked list in which
navigation is possible in both ways, either forward and backward easily
as compared to Single Linked List. Following are the important terms to
understand the concept of doubly linked list.
Link − Each link of a linked list can store a data called an element.
Next − Each link of a linked list contains a link to the next link called
Next.
Prev − Each link of a linked list contains a link to the previous link
called Prev.
Linked List − A Linked List contains the connection link to the first link
called First and to the last link called Last.
Doubly Linked List

3. Memory Representation of a doubly linked list is shown in the
following image. Generally, doubly linked list consumes more space for every
node and therefore, causes more expansive basic operations such as insertion
and deletion. However, we can easily manipulate the elements of the list since
the list maintains pointers in both the directions (forward and backward).
In the following image, the first element of the list that is i.e. 13
stored at address 1. The head pointer points to the starting address 1. Since
this is the first element being added to the list therefore the prev of the
list contains null. The next node of the list resides at address 4 therefore the
first node contains 4 in its next pointer.
We can traverse the list in this way until we find any node
containing null or -1 in its next part.

5. A B C
A doubly linked listcontain three fields: an integervalue, the
link to the next node, and the link to the previous node.
Previous Data next
NULL 11 786
786
200 400
200 656 400 786 777 NULL
Doubly Linked List Representation

6.  Doubly Linked List contains a link element called
first and last.
 Each link carries a data field(s) and two link
fields called next and prev.
 Each link is linked with its next link using its next
link.
 Each link is linked with its previous link using its
previous link.
 The last link carries a link as null to mark the end
of the list.

7.  Insertion − Adds an element at the beginning of the list.
 Deletion − Deletes an element at the beginning of the list.
 Insert Last − Adds an element at the end of the list.
 Delete Last − Deletes an element from the end of the list.
 Insert After − Adds an element after an item of the list.
 Delete − Deletes an element from the list using the key.
 Display forward − Displays the complete list in a forward manner.
 Display backward − Displays the complete list in a backward
manner.
Basic Operations ON Doubly Linked List

8. //holds theaddress of previous node
struct node
{
int data;
node*next;
node*previous;
};
.Data .next
previous.
inf

9.  As in doubly linked list, each node of the list contain double
pointers therefore we have to maintain more number of pointers in doubly
linked list as compare to singly linked list.
 There are two scenarios of inserting any element into doubly
linked list. Either the list is empty or it contains at least one element.
Perform the following steps to insert a node in doubly linked list at
beginning.
 Allocate the space for the new node in the memory. This will be
done by using the following statement.
 ptr = (struct node *)malloc(sizeof(struct node));
 Check whether the list is empty or not. The list is empty if the
condition head == NULL holds
Insertion in doubly linked list at beginning

10.  In that case, the node will be inserted as the only node of the list and
therefore the prev and the next pointer of the node will point to NULL and
the head pointer will point to this node.
 ptr->next = NULL;
 ptr->prev=NULL;
 ptr->data=item;
 head=ptr;
 In the second scenario, the condition head == NULL become false and
the node will be inserted in beginning. The next pointer of the node will
point to the existing head pointer of the node. The prev pointer of the
existing head will point to the new node being inserted.
Insertion in doubly linked list at beginning

11.  This will be done by using the following statements.
 ptr->next = head;
 head→prev=ptr;
 Since, the node being inserted is the first node of the list
and therefore it must contain NULL in its prev pointer.
Hence assign null to its previous part and make the head
point to this node.
 ptr→prev =NULL
 head = ptr
Insertion in doubly linked list at beginning

12. Insertion in doubly linked list at beginning

13.  Add a node after a given node.:
We are given pointer to a node as
prev_node, and the new node is inserted after
the given node.
Insertion in doubly linked list after given Node

14.  The new node is always added after the last node of the given Linked List.
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.
Insertion in doubly linked list At end

15. Deletion in a doubly linked list can happen at
various places in the list.
 At the beginning of the doubly linked list.
 At the end of the doubly linked list.
 At a given position in the doubly linked list.

16.  Copy the head node in some temporary node.
 Make the second node as the head node.
 The prev pointer of the head node is referenced to NULL.
 Delete the temporary node.

17.  Suppose you want to delete the second node from the list.
 Start traversing the linked list from the head until the
position = 2 of the node to be deleted.
 Let the node at the position 2 of the list be temp.
 Assign the next pointer of temp to temp's previous
node's next pointer.
 Assign the temp's prev pointer to temp's next
node's prev pointer.
 Delete the temp node.

19.  Copy the last node to a temporary node.
 Shift the last node to the second last position.
 Make the last node's next pointer as NULL.
 Delete the temporary node.

20. THANK YOU