Applications, Advantages and Disadvantages of Deque

Deque is a type of queue in which insert and deletion can be performed from either front or rear. It does not follow the FIFO rule. It is also known as double-ended queue

Operations on Deque:

Deque consists of mainly the following operations:

• Insert Front
• Insert Rear
• Delete Front
• Delete Rear

1. Insert at the Front: This operation is used to add an element at the front. If the number of elements is not exceeding the size of the deque then only insertion takes place. This operation takes constant time. Time Complexity: O(1)

2. Insert at the Rear: If the deque is not full then this function inserts the element at the back end of the queue. This operation done in O(1) time.

3. Delete from the Front: This operation is used to delete an element from the deque. If the deque is not empty then this operation will delete an element from the front end of the deque. It’s time Complexity is O(1).

4. Delete from the Rear: This operation is used to delete an element from the back end of the deque if the deque is not empty.  It’s time Complexity is O(1).

For more details regarding the operation and their implementation using circular array or doubly linked list, follow the articles about “Implementation of Deque using circular array” and “Implementation of Deque using doubly linked list“.

Properties of Deque: 

• Deque is a generalized version of the queue which allows us to insert and delete the element at both ends. 
• It does not follow FIFO (first in first out) rule.

Applications of Deque:

• It is used in job scheduling algorithms.
• It supports both stack and queue operations.
• The clockwise and anti-clockwise rotation operations in deque are performed in O(1) time which is helpful in many problems.

Real-time Application of Deque: 

• In a web browser’s history, recently visited URLs are added to the front of the deque and the URL at the back of the deque is removed after some specified number of operations of insertions at the front.
• Storing a software application’s list of undo operations.
• In graph traversal algorithms such as breadth-first search (BFS). BFS uses a deque to store nodes and performs operations such as adding or removing nodes from both ends of the deque.
• In task management systems to manage the order and priority of incoming tasks. Tasks can be added to the front or back of the deque depending on their priority or deadline.
• In queueing systems to manage the order of incoming requests. Requests can be added to the front or back of the deque depending on their priority or arrival time.
• In caching systems to cache frequently accessed data. Deques can be used to store cached data and efficiently support operations such as adding or removing data from both ends of the deque.

Advantages of Deque:

• You are able to add and remove items from the both front and back of the queue.
• Deques are faster in adding and removing the elements to the end or beginning.
• The clockwise and anti-clockwise rotation operations are faster in a deque.
• Dynamic Size: Deques can grow or shrink dynamically.
• Efficient Operations: Deques provide efficient O(1) time complexity for inserting and removing elements from both ends.
• Versatile: Deques can be used as stacks (LIFO) or queues (FIFO), or as a combination of both.
• No Reallocation: Deques do not require reallocation of memory when elements are inserted or removed.
• Thread Safe: Deques can be thread-safe if used with proper synchronization.
• Cache-Friendly: Deques have a contiguous underlying storage structure which makes them cache-friendly.

Disadvantages of Deque:

• Deque has no fixed limitations for the number of elements they may contain. This interface supports capacity-restricted deques as well as the deques with no fixed size limit.
• They are less memory efficient than a normal queue.
• Memory Overhead: Deques have higher memory overhead compared to other data structures due to the extra pointers used to maintain the double-ended structure.
• Synchronization: Deques can cause synchronization issues if not used carefully in multi-threaded environments.
• Complex Implementation: Implementing a deque can be complex and error-prone, especially if implementing it manually.
• Not All Platforms: Deques may not be supported by all platforms, and may need to be implemented manually.
• Not Suitable for Sorting: Deques are not designed for sorting or searching, as these operations require linear time.
• Limited Functionality: Deques have limited functionality compared to other data structures such as arrays, lists, or trees.