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Types of Queue in Data Structure

Last Updated on June 19, 2023 by Prepbytes

In this blog, we will learn about queue in data structure we will learn all about the queue, and operations can perform on queue. Followed by types of queue in data structure we will learn all about the types of queue in data structure with their deep explanation of all the types of queue in data structure, the corresponding operations we can perform on them, and the application of all of them.

Queue in Data Structure

Queues are a type of linear data structure that follows the First-In-First-Out (FIFO) principle. It means that the elements added first to the queue are the first to be removed. A queue can be visualized as a line where elements are placed at the end of the line (rear) and removed from the front of the line.
You can understand a queue in simple language as it is a data structure in which we add the elements from the end and the elements are removed in the same order they are added to the queue. You can understand this with a real-life example suppose you are standing in a queue for a ticket counter the person who comes first will be placed at the front of the queue and the people who came after that will join the person at the front from behind and the services will be also given in that order that means the person who comes first will get the ticket first after that and the process will continue till there is no one left in the queue or the queue is empty.

Basic Operations of Queue

There are some basic operations that we can perform on queue we will discuss all of them in this section. After this, we will discuss types of queue in data structure.

• Enqueue(): By this, we add the element to the rear end of the queue. The elements will be added after the previous element and this process will continue.
• Dequeue(): It is the opposite of enqueue this is used to remove the value from the front end of the queue it also returns the removed value.
• isEmpty(): This is a boolean operation that sees whether the queue is empty or not. If the queue is empty it will return true and if the queue is not empty it will return false.
• isFull(): This is also a boolean operation that results true or false depending on the size of the queue if the size of the queue is full it will return true otherwise it will return false.
• peek(): It will give the value of the top element of the queue or you can say that the element of the front of the queue.

Types of Queue in Data Structure

Here we will learn about types of queue in data structure with proper detail.

1. Simple Queue or Linear Queue

A simple queue is a linear data structure that follows the First-In-First-Out (FIFO) principle. It allows elements to be added to the end of the queue (rear) and removed from the front. The two main operations performed on a simple queue are enqueue (add an element to the rear) and dequeue (remove an element from the front). A simple queue can be implemented using an array or a linked list and is used in many applications, such as managing tasks in an operating system, implementing communication protocols, and simulating real-life scenarios.

This is one of the type of queue data structure and one of the first type of queue data structure that is learned by a programmer. We will now see the advantages and disadvantages of a simple queue.

This is the advantage of the first type of queue data structure.

• First-In-First-Out (FIFO) principle: Linear Queues follow the FIFO principle, ensuring that elements are processed in the order they were added.
• Easy to implement: Linear Queues are easy to implement, making them a suitable data structure for many applications.
• High efficiency for basic operations: Linear Queues provide high efficiency for inserting elements at the rear and removing elements from the front.

This is the disadvantage of the first type of queue data structure.

• Limited operations: Linear Queues only support basic operations such as enqueue, dequeue, and peek, limiting their flexibility for more complex operations.
• Memory usage: Linear Queues may consume a large amount of memory, especially if the number of elements in the queue is large.
• Performance issues: Performance issues can arise when inserting and removing elements, especially when the size of the queue is large.

2. Circular Queue

A circular queue is a type of queue data structure that uses a circular buffer to store elements. Unlike a simple queue, which has a fixed size, a circular queue allows the use of a circular buffer that can be dynamically resized. In a circular queue, the front and rear pointers "wrap around" the buffer after reaching the end, allowing the reuse of space that has been freed up by dequeue operations.

The main operations performed on a circular queue are enqueue and dequeue, similar to a simple queue. However, in a circular queue, when an element is enqueued and the rear pointer reaches the end of the buffer, it wraps around to the beginning, allowing the reuse of memory. Similarly, when an element is dequeued and the front pointer reaches the end of the buffer, it also wraps around to the beginning.

A circular queue is useful when there is a need to efficiently manage a limited amount of memory, such as in real-time systems. It also solves the problem of overflow in a simple queue, where the queue becomes full and new elements cannot be added.

In conclusion, a circular queue is a type of queue data structure that uses a circular buffer to store elements. It provides a solution for efficiently managing a limited amount of memory and eliminates the problem of overflow in a simple queue.

Advantage of using a Circular queue

Here we will discuss the advantages of using a circular queue which is one of a types of queue in data structure.

• Memory utilization: In a circular queue, memory utilization is better as compared to a linear queue. This is because a circular queue reuses the memory that is freed up after the front pointer reaches the end of the queue.
• Easy to implement: A circular queue is easier to implement compared to a linear queue as it does not require the creation of a new queue every time the rear pointer reaches the end of the queue.
• Efficient for real-time systems: Circular queues are ideal for real-time systems where elements are constantly being added and removed. This is because the front and rear pointers in a circular queue move in a circular fashion, making the insertion and deletion of elements efficient.

Here we will discuss the disadvantages of using a circular queue which is one of a types of queue in data structure.

• Overhead of pointers: Circular queues require two pointers, front and rear, to keep track of the elements in the queue. This increases the overhead as compared to a linear queue, where only one pointer is required.
• Complex algorithms: The algorithms for inserting and deleting elements in a circular queue can be complex as compared to a linear queue.
• Pointer maintenance: In a circular queue, it is necessary to keep track of both the front and rear pointers, which can be time-consuming and prone to errors.

Operations on Circular Queue

Here we will discuss the operations that we can perform on circular queue which is one of the types of queue in data structure.

• front(): front is used to track the first element of the queue.
• Enqueue: This operation is used to Insert an element at the end of the queue.
• rear(): rear is used to track the last element of the queue.
• Dequeue: This operation is used to remove and return an element from the front of the queue.

3. Priority Queue

A priority queue is one of the types of queue in data structure in which each element is assigned a priority and the elements are served in order of priority. This means that the highest priority element is served first and the lowest priority element is served last. The priority of each element can be determined based on different criteria such as arrival time, size, or value. The priority queue can be implemented using an array, linked list, or a binary heap. The main advantage of using a priority queue is that it enables efficient processing of elements based on their priority. This makes it useful in many real-world applications such as scheduling processes in an operating system, implementing shortest-path algorithms in graph theory, or implementing event-driven simulations.

In the priority queue, the insertion is done based on the arrival time whereas the deletion is done based on the priority assigned.

Here we will discuss the advantage of using a priority queue which is one of the types of queue in data structure.

• Improved Performance: The priority queue ensures that the most important task is executed first, which results in improved performance and quick completion of important tasks.
• Dynamic Resource Allocation: The priority queue helps in dynamic resource allocation, as it assigns higher priority to tasks that are more important, ensuring that the resources are utilized effectively.
• Fair Allocation of Resources: A priority queue helps in the fair allocation of resources as it assigns higher priority to tasks that need more resources, and lower priority to tasks that need fewer resources.

Here we will discuss the disadvantage of using a priority queue which is one of the types of queue in data structure.

• Complexity: The implementation of a priority queue can be complex and difficult to understand, especially for a beginner.
• Unpredictable Performance: The performance of a priority queue is dependent on the priority assigned to each task, and it can be unpredictable as the priority of tasks may change dynamically.
• Overhead: The priority queue adds an overhead to the system as it requires additional memory to store the priority information for each task, and additional processing time to assign priorities and rearrange the queue.

Uses of Priority Queue

• The priority queue is used in memory management.
• The priority queue is used in CPU Scheduling.
• Also used in the Traffic system.

Implementation of Priority Queue:

The priority queue is one of the type of queue in data structure and is implemented in the following ways:

• Using Arrays.
• Using Heap data structure
• Using Binary Search Tree

4. Deque

Deque (Double Ended Queue) is a linear data structure that is also one of the types of queue in data structure where elements can be inserted and removed from both the end of queue whether the front or the rear end of the queue. It’s a hybrid between a stack and a queue, as it supports both LIFO (Last In First Out) and FIFO (First In First Out) operations. A deque allows efficient insertion and deletion at both the front and the end of the queue, making it a versatile data structure. Some applications of deque include searching algorithms, computer memory management, and graph algorithms.

Deque supports insertion and deletion operations on both ends, making it suitable for usage as both a queue and a stack. Deque may be compared to a stack since both insertion and deletion can only be done from one end of a stack, which adheres to the LIFO (Last In First Out) concept. Deque does not adhere to the FIFO principle and allows both insertion and deletion to be carried out from one end.

Type of Deque

Dequeue is one of the types of queue in data structure and it further has two types that we will discuss here.

• Input Restricted deque: As the name suggests, in input restricted deque, insertion operation can be performed at only one end whereas deletion operation can be done from both ends.
• Output Restricted deque: In output restricted deque, deletion operation can be performed at a single end whereas insertion operation can be performed at both ends.

Here we will discuss the advantage of using a Deque which is one of the types of queue in data structure.

• Flexibility: Deques allow inserting and removing elements from both front and rear, providing great flexibility in terms of inserting and removing elements.
• Better Performance: In a deque, elements can be added and removed at both ends in constant time, making deques more efficient than a single-ended queue.
• Applications: Deques are used in various algorithms and applications such as graph algorithms, simulations, and computer games.

Here we will discuss the disadvantage of using a Deque which is one of the types of queue in data structure.

• Space Complexity: Deques use more memory than simple queues because they have to store two pointers for front and rear, leading to a higher space complexity.
• Implementation: Implementing a deque can be a challenging task as it requires keeping track of both front and rear pointers.
• Complexity: Deques are more complex in nature as compared to simple queues, making them difficult to understand and implement for some people.

Applications of Queue

As of now, we have discussed all types of queue in data structure. Now we will discuss the applications of Queue.