Data Structure - Doubly Linked List
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.
LinkedList A Linked List contains the connection link to the first link called First and to the last link called Last.
Doubly Linked List Representation
As per the above illustration, following are the important points to be considered.
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.
Basic Operations
Following are the basic operations supported by a list.
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.
Insertion Operation
Following code demonstrates the insertion operation at the beginning of a doubly linked list.
Example
//insert link at the first location void insertFirst[int key, int data] { //create a link struct node *link = [struct node*] malloc[sizeof[struct node]]; link->key = key; link->data = data; if[isEmpty[]] { //make it the last link last = link; } else { //update first prev link head->prev = link; } //point it to old first link link->next = head; //point first to new first link head = link; }Deletion Operation
Following code demonstrates the deletion operation at the beginning of a doubly linked list.
Example
//delete first item struct node* deleteFirst[] { //save reference to first link struct node *tempLink = head; //if only one link if[head->next == NULL] { last = NULL; } else { head->next->prev = NULL; } head = head->next; //return the deleted link return tempLink; }Insertion at the End of an Operation
Following code demonstrates the insertion operation at the last position of a doubly linked list.
Example
//insert link at the last location void insertLast[int key, int data] { //create a link struct node *link = [struct node*] malloc[sizeof[struct node]]; link->key = key; link->data = data; if[isEmpty[]] { //make it the last link last = link; } else { //make link a new last link last->next = link; //mark old last node as prev of new link link->prev = last; } //point last to new last node last = link; }To see the implementation in C programming language, please click here.