20 Doubly Linked List Interview Questions and Answers

Doubly linked lists are a type of data structure that allows for efficient insertion and deletion of data. They are often used in programming interviews to test a candidate’s ability to think through a problem and develop a solution. If you are preparing for a programming interview, it is important to review common doubly linked list questions and practice your responses. In this article, we discuss the most commonly asked questions about doubly linked lists and provide example responses.

Doubly Linked List Interview Questions and Answers

Here are 20 commonly asked Doubly Linked List interview questions and answers to prepare you for your interview:

1. What are Doubly Linked Lists?

A doubly linked list is a type of linked list in which each node has two pointers, one pointing to the previous node and one pointing to the next node. This allows for traversal of the list in both directions.

2. Can you explain what a doubly linked list is and how it differs from a singly linked list?

A doubly linked list is a type of linked list in which each node has two pointers, one pointing to the previous node and one pointing to the next node. This allows for traversal in both directions. A singly linked list, on the other hand, only has a single pointer per node, meaning that traversal is only possible in one direction.

3. How do you add an item to the end of a doubly linked list?

You would add an item to the end of a doubly linked list by creating a new node with the data you want to add, and then linking that node to the last node in the list. The new node would then become the new last node in the list.

4. How can you delete a node in a doubly linked list given only access to that node?

In order to delete a node in a doubly linked list, you need to have access to both the node that you want to delete as well as the node that precedes it in the list. Once you have access to both of those nodes, you can simply adjust the pointers so that the node that precedes the one you want to delete now points to the node that follows the one you want to delete, and vice versa.

5. How does a circular doubly-linked list differ from other types of doubly linked lists?

In a circular doubly-linked list, the last node in the list is linked to the first node in the list. This creates a loop, so that you can move through the list from the first node to the last node and back again endlessly. Other types of doubly linked lists do not have this loop, so you can only move through the list in one direction.

6. Is it possible to create a doubly linked list with zero nodes? If yes, then how?

Yes, it is possible to create a doubly linked list with zero nodes. This can be accomplished by setting the head and tail pointers to null.

7. Is it possible to have both head and tail pointers point to NULL at the same time? What about when traversing forward or backward through a doubly linked list?

Yes, it is possible for both head and tail pointers to point to NULL at the same time. This would happen if the doubly linked list is empty. When traversing forward through a doubly linked list, the head pointer will point to the first node in the list and the tail pointer will point to the last node in the list. When traversing backward through a doubly linked list, the head pointer will point to the last node in the list and the tail pointer will point to the first node in the list.

8. Why would you use a doubly linked list instead of a single linked list?

A doubly linked list offers a few advantages over a single linked list. First, because each node has pointers to both the next and previous nodes in the list, it is easier to navigate backwards through a doubly linked list than a single linked list. Additionally, because each node has a pointer to both the next and previous nodes, it is easier to insert and delete nodes from a doubly linked list than a single linked list.

9. Are there any disadvantages to using a doubly linked list over a singly linked list?

The main disadvantage of using a doubly linked list over a singly linked list is that it requires twice as much memory to store the same amount of data. This is because each node in a doubly linked list contains two pointers (one pointing to the previous node and one pointing to the next node), whereas each node in a singly linked list only contains one pointer.

10. What’s the difference between deleting a node from the front or back of a doubly linked list?

If you delete a node from the front of a doubly linked list, then you will need to update the head pointer to point to the new first node in the list. If you delete a node from the back of the list, then you will need to update the tail pointer to point to the new last node in the list.

11. Is it possible to make all nodes in a doubly linked list point to the same previous element? What about the next element?

It is not possible to make all nodes in a doubly linked list point to the same previous element, as this would break the structure of the list. However, it is possible to make all nodes in a doubly linked list point to the same next element. This would result in a circular linked list.

12. Is it possible to sort a doubly linked list? If yes, then how?

Yes, it is possible to sort a doubly linked list. There are a few different ways to do this, but one common approach is to use a merge sort algorithm. This will involve breaking the list down into smaller sublists, sorting each of those sublists, and then merging the sorted sublists back together into one overall sorted list.

13. What are some ways to print out the contents of a doubly linked list?

There are a few ways to print out the contents of a doubly linked list. One way is to simply iterate through the list, starting at the head, and print out each element as you go. Another way is to reverse the list, and then print it out in reverse order. Finally, you could also print out the list in reverse order starting from the tail.

14. What are some real-world applications where doubly linked lists might be used?

One potential application for a doubly linked list is a web browser history feature, where users can click “back” and “forward” buttons to move between previously visited web pages. Another potential application is a music player, where users can create a playlist of songs and then skip forward and backward between them.

15. What are some advantages of doubly linked lists over arrays?

One advantage of doubly linked lists over arrays is that they allow for easier insertion and deletion of elements. This is because with an array, all elements after the one being inserted or deleted would need to be shifted in order to make room or close the gap. With a doubly linked list, there are pointers to both the next and previous elements, so no shifting is necessary.

Another advantage of doubly linked lists is that they can be traversed in either direction. With an array, you can only move forward through the elements. With a doubly linked list, you can move both forward and backward, which can be helpful in some situations.

16. What is the maximum number of elements that can be stored in a doubly linked list?

The maximum number of elements that can be stored in a doubly linked list is 2^64 – 1, or 4294967295. This is due to the fact that each node in a doubly linked list requires two pointers, one for the next node and one for the previous node.

17. What are the main differences between vectors, stacks, queues, and doubly linked lists?

The main differences between vectors, stacks, queues, and doubly linked lists are their size, their structure, and their functionality. Vectors are arrays that can grow and shrink as needed, while stacks and queues are fixed-size collections. Stacks are last-in-first-out data structures, while queues are first-in-first-out. Doubly linked lists are linked lists that have links going in both directions, while singly linked lists only have links going in one direction.

18. What are the different insertion methods for doubly linked lists?

There are three different insertion methods for doubly linked lists:

1. Inserting at the head of the list
2. Inserting at the tail of the list
3. Inserting in the middle of the list

19. Which one of these do you think is faster: inserting an element at the beginning, middle, or end of a doubly linked list?

Inserting an element at the beginning of a doubly linked list is the fastest option. This is because you only need to update the pointers for the head and tail nodes, and you do not need to traverse the entire list to find the correct insertion point. Inserting an element in the middle or end of a list requires traversing the list to find the correct insertion point, which takes more time.

20. What are some common algorithms used on doubly linked lists?

Some common algorithms used on doubly linked lists include insertion, deletion, searching, and sorting.