Data Structures and Algorithms (Some Questions for You - Answer to Question 16) - Tirthankar Pal - MBA from IIT Kharagpur, GATE, GMAT, IIT Written Test, Interview were a part of MBA Entrance, B.S. in Computer Science from NIELIT

Draw a circular doubly linked list. Give an advantage of a circular doubly linked list.

Circular Doubly Linked List has properties of both doubly linked list and circular linked list in which two consecutive elements are linked or connected by the previous and next pointer and the last node points to the first node by the next pointer and also the first node points to the last node by the previous pointer.

Following is the representation of a Circular doubly linked list node in C/C++: 

• C

// Structure of the node struct node {     int data;       // Pointer to next node     struct node* next;       // Pointer to previous node     struct node* prev; };

 

Circular Doubly Linked LIst

Insertion in Circular Doubly Linked List:

1. Insertion at the end of the list or in an empty list:

A node(Say N) is inserted with data = 5. So, the previous pointer of N points to N and the next pointer of N also points to N. But now start pointer points to the first node of the list.

Insertion in an empty list

2. List initially contains some nodes, start points to the first node of the List: 

A node(Say M) is inserted with data = 7, so the previous pointer of M points to the last node, the next pointer of M points to the first node and the last node’s next pointer points to this M node, and first node’s previous pointer points to this M node.

Insertion at the end of list

Below is the implementation of the above operations:

• C++
• Java
• Python3
• C#
• Javascript

// Function to insert at the end void insertEnd(struct Node** start, int value) {     // If the list is empty, create a single node     // circular and doubly list     if (*start == NULL) {         struct Node* new_node = new Node;         new_node->data = value;         new_node->next = new_node->prev = new_node;         *start = new_node;         return;     }       // If list is not empty       /* Find last node */     Node* last = (*start)->prev;       // Create Node dynamically     struct Node* new_node = new Node;     new_node->data = value;       // Start is going to be next of new_node     new_node->next = *start;       // Make new node previous of start     (*start)->prev = new_node;       // Make last previous of new node     new_node->prev = last;       // Make new node next of old last     last->next = new_node; }

3. Insertion at the beginning of the list: 

To insert a node at the beginning of the list, create a node(Say T) with data = 5, T next pointer points to the first node of the list, T previous pointer points to the last node of the list, last node’s next pointer points to this T node, first node’s previous pointer also points this T node and at last don’t forget to shift ‘Start’ pointer to this T node.

Insertion at the beginning of the list

Below is the implementation of the above operation:

• C++
• Java
• Python3
• C#
• Javascript

// Function to insert Node at the beginning // of the List, void insertBegin(struct Node** start, int value) {     // Pointer points to last Node     struct Node* last = (*start)->prev;       struct Node* new_node = new Node;     new_node->data = value; // Inserting the data       // setting up previous and next of new node     new_node->next = *start;     new_node->prev = last;       // Update next and previous pointers of start     // and last.     last->next = (*start)->prev = new_node;       // Update start pointer     *start = new_node; }

4. Insertion in between the nodes of the list: 

To insert a node in between the list, two data values are required one after which new node will be inserted and another is the data of the new node.

Insertion in between other nodes

Below is the implementation of the above operation:

• C++
• Java
• Python3
• C#
• Javascript

// Function to insert node with value as value1. // The new node is inserted after the node with // with value2 void insertAfter(struct Node** start, int value1,                  int value2) {     struct Node* new_node = new Node;     new_node->data = value1; // Inserting the data       // Find node having value2 and next node of it     struct Node* temp = *start;     while (temp->data != value2)         temp = temp->next;     struct Node* next = temp->next;       // insert new_node between temp and next.     temp->next = new_node;     new_node->prev = temp;     new_node->next = next;     next->prev = new_node; }

Following is a complete program that uses all of the above methods to create a circular doubly linked list.  

• C++
• Java
• Python3
• C#
• Javascript

// C++ program to illustrate inserting a Node in // a Circular Doubly Linked list in begging, end // and middle #include <bits/stdc++.h> using namespace std;   // Structure of a Node struct Node {     int data;     struct Node* next;     struct Node* prev; };   // Function to insert at the end void insertEnd(struct Node** start, int value) {     // If the list is empty, create a single node     // circular and doubly list     if (*start == NULL) {         struct Node* new_node = new Node;         new_node->data = value;         new_node->next = new_node->prev = new_node;         *start = new_node;         return;     }       // If list is not empty       /* Find last node */     Node* last = (*start)->prev;       // Create Node dynamically     struct Node* new_node = new Node;     new_node->data = value;       // Start is going to be next of new_node     new_node->next = *start;       // Make new node previous of start     (*start)->prev = new_node;       // Make last previous of new node     new_node->prev = last;       // Make new node next of old last     last->next = new_node; }   // Function to insert Node at the beginning // of the List, void insertBegin(struct Node** start, int value) {     // Pointer points to last Node     struct Node* last = (*start)->prev;       struct Node* new_node = new Node;     new_node->data = value; // Inserting the data       // setting up previous and next of new node     new_node->next = *start;     new_node->prev = last;       // Update next and previous pointers of start     // and last.     last->next = (*start)->prev = new_node;       // Update start pointer     *start = new_node; }   // Function to insert node with value as value1. // The new node is inserted after the node with // with value2 void insertAfter(struct Node** start, int value1,                  int value2) {     struct Node* new_node = new Node;     new_node->data = value1; // Inserting the data       // Find node having value2 and next node of it     struct Node* temp = *start;     while (temp->data != value2)         temp = temp->next;     struct Node* next = temp->next;       // insert new_node between temp and next.     temp->next = new_node;     new_node->prev = temp;     new_node->next = next;     next->prev = new_node; }   void display(struct Node* start) {     struct Node* temp = start;       printf("\nTraversal in forward direction \n");     while (temp->next != start) {         printf("%d ", temp->data);         temp = temp->next;     }     printf("%d ", temp->data);       printf("\nTraversal in reverse direction \n");     Node* last = start->prev;     temp = last;     while (temp->prev != last) {         printf("%d ", temp->data);         temp = temp->prev;     }     printf("%d ", temp->data); }   /* Driver program to test above functions*/ int main() {     /* Start with the empty list */     struct Node* start = NULL;       // Insert 5. So linked list becomes 5->NULL     insertEnd(&start, 5);       // Insert 4 at the beginning. So linked     // list becomes 4->5     insertBegin(&start, 4);       // Insert 7 at the end. So linked list     // becomes 4->5->7     insertEnd(&start, 7);       // Insert 8 at the end. So linked list     // becomes 4->5->7->8     insertEnd(&start, 8);       // Insert 6, after 5. So linked list     // becomes 4->5->6->7->8     insertAfter(&start, 6, 5);       printf("Created circular doubly linked list is: ");     display(start);       return 0; }

Output

Created circular doubly linked list is: 
Traversal in forward direction 
4 5 6 7 8 
Traversal in reverse direction 
8 7 6 5 4 

Time Complexity: O(N)
Auxiliary Space: O(1), As constant extra space is used.

Advantages of circular doubly linked list: 

• The list can be traversed from both directions i.e. from head to tail or from tail to head.
• Jumping from head to tail or from tail to head is done in constant time O(1).
• Circular Doubly Linked Lists are used for the implementation of advanced data structures like the Fibonacci Heap.

Disadvantages of circular doubly linked list: 

• It takes slightly extra memory in each node to accommodate the previous pointer.
• Lots of pointers are involved while implementing or doing operations on a list. So, pointers should be handled carefully otherwise data of the list may get lost.

Applications of Circular doubly linked list:

• Managing song playlists in media player applications.
• Managing shopping carts in online shopping.

Tirthankar Pal

MBA from IIT Kharagpur with GATE, GMAT, IIT Kharagpur Written Test, and Interview
2 year PGDM (E-Business) from Welingkar, Mumbai
4 years of Bachelor of Science (Hons) in Computer Science from the National Institute of Electronics and Information Technology
Google and Hubspot Certification
Brain Bench Certification in C++, VC++, Data Structure and Project Management
10 years of Experience in Software Development out of that 6 years 8 months in Wipro
Selected in Six World Class UK Universities:-
King's College London, Durham University, University of Exeter, University of Sheffield, University of Newcastle, University of Leeds