Types of Queue in Data Structure – The 2024 Guide

Did you know that without the use of queues in the data structure, data won’t go in a specific order? Queue is what enables operations to go in a certain way, although this is dependent on the element you insert in it. A queue is open on both ends, one end of the queue is always used to input data (enqueue), whereas the other end of the queue is used to delete data (dequeue). Let’s explore the different types of queues in Data Structure and how to use them below.

What is Queue in Data Structure?

A queue is a structure that allows elements to go a particular way through the use of FIFO (i.e. first in, first out). This means that data comes in first from the tail of the queue (rear end) and goes out through the head of the queue (front end) systematically. In essence, a queue ensures that data comes in and goes out in an organized manner. You can take a data structure course and algorithms to have a better understanding of it in programming.

Also Read: Types of Data Structure

6 Different Types of Queues in Data Structure

We will explain the different types of queues in Data Structures below:

1. A Double-Ended Queue

A double-ended queue is also called a deque. It works from both ends, and it can take or remove data at both ends (the rear and front). This queue consists of an input-restricted deque and an output-restricted deque. 

A double-ended queue does not work on the FIFO principle because it works at both ends. In essence, it works in a clock and anti-clockwise rotation which means that you can use it in any given situation. You can either add or remove an element from the front or rear end. Deque is employed to increase data processing versatility in applications where pieces must be handled in numerous directions. Search algorithms are based on deque.

2. Circular Queue

This queue mainly works with the principle of the FIFO. The data structure of a circular queue works in a sequenced manner, which enables data to come through the first position and back to the last in a systematic order. It is also called the ring buffer because the last position takes elements back to the first in a circular manner. Below are several cases where this queue can be used:

• Traffic System: Whenever a system with computer-controlled traffic is queued, the queue switches on the traffic light at the time it is set for.
• CPU Scheduling: This enables a processing system to systematically keep a processed queue until it is time for them to be executed or wait for a certain command to be executed.
• Memory Management: A circular queue can be used when you have a free space during an ordinary queue.

If an application needs data to go in a circular motion through both ends, the circular queue can be used. CPU scheduling and memory management are two instances where the circular queue is used. A circular queue is identical to a linear queue, except that the end of the queue is connected back to the front of the queue.

3. Priority Queue

The priority queue is unique. Elements in this queue are set in priority whereby the element with the least amount of priority leaves the queue first. Majorly, a priority queue is used to schedule the CPU algorithm. Priority queue functions in two ways, which are explained below:

• Ascending Priority Queue: In this queue, you can add elements in a random manner such as 6, 8, 4 but to delete an element you can only delete from the least number which is 4, 6, 8.
• Descending Priority Queue: This is similar to an ascending queue, but it works in the opposite manner while deleting. Elements can be added randomly, but you can remove only the highest number in a given queue. Assuming the given queue is 6, 8, and 7 elements, deleting an element from this queue will start from 8, 7, and 6 respectively.

These queues are used in applications where specific tasks or data components must be completed more quickly. Operating system job scheduling and network packet scheduling are two examples of the use of priority queues. In a priority queue, the components of higher priority are processed before components of lower importance. 

4. Simple Queue

This is the basic type of queue in DS and it works on the FIFO principle. The insertion of elements comes through the rear end and goes out through the front. The best way to implement a simple queue is when you do not want data to be processed immediately. It can be used to schedule a process and maximize data management.

5. Concurrent Queue

A concurrent queue is a type of queue that prevents multiple threads from changing their state simultaneously, which could lead to discrepancies. It offers protection against potential clashes occurring between different operations on the same data by making sure only one thread can modify it at any given time. 

Concurrent queues are employed in multi-threaded systems, where data must be shared safely between all processes. Database transactions and web server requests are two examples.

6. Linear Queue

A linear queue is sometimes referred to as just a queue because it moves in a straight line which employs the principle of the FIFO. That means data that comes in goes out first. Therefore, in applications where data elements must be handled in the linear order in which they are received, linear queues are utilized. Printer queues and message queues are two examples of linear queues.

What are the Common Challenges of Using Queue?

Below are the basic issues associated with a queue:

• Due to the large memory queue used during data processing. A queue can crash and damage a system.
• When many processes are in the same queue at the same time, synchronization problems might occur. Data corruption, race situations, and other mistakes might come from this.
• When many threads or processes wait for each other to release resources, a deadlock occurs, and none of the threads may progress. This is possible while utilizing concurrent queues and can result in system crashes.
• When a queue reaches its full capacity and cannot receive any more components, it is said to be overflowing. This might result in data loss and application failures.
• In priority queues, priority inversion happens when a low-priority task has a resource that a high-priority process requires. This can create processing delays and have an impact on system performance.
• The size of the queue, the frequency of access, and the type of operations done on the queue can all have an influence on queue performance. Slower system performance and a worse user experience might result from poor queue performance.

Conclusion

We hope you have gained a comprehensive knowledge of the various types of queues that we have listed above. It is important to understand when to use the different types of queues in Data Structure, as the knowledge will enable you to insert or delete elements at either end of the queue depending on the task and what you wish to achieve.