Deque in C#

C# Deque means double-ended queue. It is a linear data structure that allows us to add or remove elements from both the front and the end. A deque is more flexible than the normal queue where we can only add elements from the back and remove them from the front.

• Elements can be added or removed from both the front and end.
• The deque can grow and shrink dynamically.
• We can use deque as a Stack or Queue depending upon the use cases.

Example: This example demonstrates how to add elements to both the front and the back of the deque

Elements in the Deque:
30
20
10
50

Why use a Deque?

Deque is very useful in scenarios where we need to manage the data from both the ends. Some of the common applications of deque are listed below:

• Job Scheduling: Managing tasks with varying priorities.
• Sliding Window Algorithms: Solving problems like finding the maximum in a subarray.
• Breadth-First Search (BFS): Traversing graphs or trees.

Types of Deque

The below diagram demonstrates the types of deque in C#.

• Input-Restricted deque: In this, insertion is allowed only at one end, but deletion can be done from both ends.
• Output-Restricted deque: In this, deletion is allowed only at one end, but insertion can be done from both ends.
• Double-Ended deque: In this, insertion and deletion are allowed at both ends.

Declaration of Deque

In C#, there is no built-in deque class. We can create deque with the help of LinkedList<T> class or by using Queue<T> class.

Note: Queue<T> can also create a deque, but it is not ideal for operation at both the ends due to limitations.

Using LinkedList<T> (Recommended Approach)

A LinkedList<T> is a good choice for a deque because it lets us add or remove items quickly from both the front and back.

Declaration of deque using LinkedList<T>

LinkedList<int> deque = new LinkedList<int>();

Example: This example, demonstrates how to add elements to both the front and back and then iterating through the list

Deque Elements:
30
20
10
40
50

Implementing Deque in C#

C# provides Three approaches to implement deque in C#, we are going to discuss about each approach one by one

1. Implementing Deque using Arrays

An Array-based deque can be implemented by managing a fixed-size array and keeping track of front and rear pointers.

Implementation:

40 30 10 20 
Dequeue from front: 40
Dequeue from rear: 20
30 10 

2. Implementing Deque using LinkedList

LinkedList<T> class is an ideal choice for deque because it allows fast insertion and deletion operations from both ends. The LinkedList<T> stores elements in a doubly-linked list, both ends can be accessed and modified in constant time O(1).

Implementation:

Output:

3. Implementing Deque Using List<T>

A list<T> is dynamic array, it can efficiently access elements by index. This approach is less efficient for the front operations (add/remove) compared to the LinkedList<T> approach but can still be useful for small lists.

Implementation:

10
30

Performing Various Operations on Deque

1. Adding Elements to the Front

We can use the EnqueueFront() to add elements to the front of the deque.

Example: This example demonstrates how to insert elements to the front of the deque.

Output:

2. Adding Element to the Rear

We can use the EnqueueRear() to add elements to the end of the deque.

Example:

Output:

3. Removing Elements from the Front

We can use the dequeFront() method to remove elements from the front of the deque.

Example:

Output:

4. Removing Elements from the Rear

We can use the dequeRear() method to remove elements from the end of the deque.

Example:

Output: