Types of Queues and their Applications

Queue, like Stack, is a linear structure in which actions are conducted in a certain order. First in, first out is the order (FIFO). Any line of consumers for a resource in which the consumer who arrived first gets serviced first is an example of a queue. In programming, a queue is an important data structure.

In this article, we are going to discuss the different types of queues along with their applications.

Different Types of Queues

There are five types of queues that are utilised in various contexts. These are:

1. Circular Queue

The last node of a circular node is connected to the initial node. Because all ends are linked to one another, it is also known as a ring buffer. Insertion occurs at the head of the queue, while deletion occurs at the back. This queue is typically utilised in the following cases:

• Memory Management: In the case of regular queues, unused memory locations might be employed in circular queues.
• Circular queues are employed in a computer-controlled traffic system to turn on traffic lights one by one according to the timer.
• CPU Scheduling: Operating systems frequently keep a queue of processes ready to execute or waiting for a certain event to occur.

2. Input restricted queue

In this form of Queue, the input can be collected from one side only (rear) and deletion of elements may be done from both sides(front and rear) (front and rear). This type of queue does not adhere to the FIFO principle (first in first out). This queue is used when data consumption must be in FIFO order but there is a requirement to discard recently added data for various reasons, such as irrelevant data, performance issues, and so on.

3. Priority Queue

The nodes in a priority queue will have a predetermined priority in the priority queue. The node with the lowest priority will be removed from the queue first. Insertion occurs in the sequence in which the nodes arrive. Priority queue applications include Dijkstra’s quickest route method, Prim’s algorithm, and data compression techniques such as Huffman coding.

Priority Queues are classified into two sorts. These are:

• Ascending Priority Queue:
  Any element can be added, but only the smallest element can be deleted. Assume there is an array with the entries 4, 2, 8 in the same order. So, while putting the components, the order will be 2, 4, 8, but after removing them, the order will be 2, 4, 8.
• Descending priority Queue:
  Elements can be added freely, but only the largest member can be removed from the provided Queue first. Assume there is an array with the entries 4, 2, 8 in the same order. So, while putting the components, the order will be 8, 4, 2, but after removing them, the order will be 8, 4, 2.
  

4. Output restricted Queue

In this sort of Queue, input may be collected from both sides (back and front), however element deletion can only be done from one (front). This queue is used when the inputs must be executed in a certain sequence, and the input can even be placed first so that it is done first.

5. Double ended queue

A Double Ended Queue is a Queue data structure in which insertion and deletion operations are carried out at both ends (front and rear). That is, we may insert at both the front and back places and remove at both the front and back positions. Since Deque supports both stack and queue operations, it may be used as both. 

Applications of Queue

Queues have a wide range of practical uses, including:

• Printer Spooling

1. A printer may receive multiple print requests in a short period of time. 
2. The rate at which these requests are received is much faster than the rate they are processed at. 
3. As a result, a temporary storage mechanism is required to store these requests in the order of their arrival. 
4. A queue is the best choice in this case, storing the print requests so that they are processed on a first-come-first-served basis.

• CPU Scheduling

1. A CPU can only handle one request at a time.
2. The pace at which the CPU receives requests is typically substantially faster than the rate at which the CPU processes requests.
3. As a result, the requests are temporarily held in a queue in the order in which they arrive.
4. When the CPU becomes available, it retrieves the requests from the queue.
5. When a request is completed, its reference is removed from the queue.
6. The CPU then receives the next request in the sequence, and the process is repeated.

• Mail service

1. Many transactions in many organisations are carried out by mail.
2. If the mail server fails and someone sends you an email, the email is returned to the sender.
3. Many businesses use a mail backup service to avoid this type of catastrophe.
4. When there is a problem with the mail server that prevents messages from being sent, the mail is routed to the backup server.
5. The backup server briefly saves the emails in a queue.
6. When the mail server is operational, all messages are delivered to the recipient in the order in which they came.

• Keyboard buffering

1. Queues are used to save keystrokes while you write on the keyboard.
2. When you input data into the keyboard, it is not always instantly shown on the screen.
3. This is because, during that time, the processor might be busy doing some other task.
4. In this case, the data is temporarily kept in a queue until it is read by the processor.
5. When the CPU is free, all keystrokes are read in the order received and shown on the screen.

Conclusion

All types of queues are very important in data structure. The queue has five different types in the data structure, i.e., circular queue, priority queue, input restricted queue, output restricted queue, double ended queue. Queue also has a wide range of applications in data structures like keyboard buffering, mail service, CPU scheduling, printer spooling, etc.