# What Are the Types of Queue in Data Structure?

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Angela Bailey

In data structures, a queue is a collection of elements that follows the FIFO (First-In-First-Out) principle. It is similar to a real-life queue where the first person to join is the first one to leave. In this article, we will explore the various types of queues in data structure and understand their characteristics.

## 1. Simple Queue

A simple queue is the most basic type of queue.

It follows the FIFO principle and has two main operations: enqueue (adding an element to the end of the queue) and dequeue (removing an element from the front of the queue). The elements are added at one end and removed from the other end.

## 2. Circular Queue

A circular queue, also known as a ring buffer, is an extension of a simple queue with a fixed size.

It overcomes the limitation of a simple queue where empty spaces are wasted once an element is dequeued. In a circular queue, when an element is dequeued, its position becomes available for future enqueue operations.

### Main advantages of using a circular queue:

• Efficient memory utilization: A circular queue optimizes memory usage by reusing empty spaces.
• Better performance: Enqueue and dequeue operations in a circular queue are faster compared to other types.

## 3. Priority Queue

A priority queue assigns priorities to each element in the queue.

The elements are arranged based on their priority rather than their order of arrival. Elements with higher priorities are dequeued before elements with lower priorities.

### Main applications of a priority queue:

• Operating systems: Priority queues are used for process scheduling, where processes with higher priorities get executed first.
• Dijkstra’s algorithm: Priority queues are essential in graph algorithms like Dijkstra’s algorithm to determine the shortest path.

## 4. Double Ended Queue (Deque)

A double ended queue, commonly known as a deque, is a queue that allows insertion and deletion at both ends.

It can be considered as a combination of a stack and a queue, as well as a circular queue. Deques have the following operations:

• EnqueueFront: Adds an element to the front of the deque.
• EnqueueRear: Adds an element to the rear of the deque.
• DequeueFront: Removes an element from the front of the deque.
• DequeueRear: Removes an element from the rear of the deque.

### Main advantages of using a double ended queue:

• Versatility: Deques can be used as both stacks and queues based on requirements.
• Efficient data manipulation: Insertion and deletion can be performed efficiently at both ends.

In conclusion, queues play a crucial role in various computer science applications. Whether it’s managing processes in an operating system or implementing algorithms, understanding different types of queues helps in choosing the right data structure for the job.