Queue in Data Structure

What is a Queue?

Queues are linear structures that allow elements to be inserted from the rear and deleted from the front. The queue elements are ordered in the FIFO (First-In, First-Out) order.

Representation of a queue in data structures

We know that a queue can be accessed from both sides, deleting from the front and inserting from the back or rear.

Working of Queue in Data Structures

• Two pointers are marking two ends, FRONT and REAR.
• FRONT records the queue's first element.
• REAR tracks the queue's last member.
• Initially, set the values of FRONT and REAR to -1.
• After that, do the basic operations using the algorithms listed above.

Different Types of Queues in Data Structures

• Simple Queue/Linear Queue: Elements are added at the back and withdrawn at the front, in the FIFO sequence.
• Circular Queue: Similar to a simple queue, except the last member connects to the first, resulting in a circular structure for efficient memory usage.
• Priority Queue: Each element is assigned a priority; the highest priority elements are eliminated first, allowing for prioritized processing.
• Deque (Double-Ended Queue): Elements may be added or withdrawn from both the front and back ends of the queue.

Implementation of Queue

There are two main methods for implementing a queue:

1. Array
2. Linked List

1. Array

Array-based queues have a fixed size, which means you can only add or remove elements up to the length of the array.

2. Linked List

Linked list-based queues have no defined size, so you can add and remove as many components as you wish.

Basic Operations of Queue

• Enqueue: Insert an element at the end of the queue.
• Dequeue: Remove an item from the queue's front.
• IsEmpty: Determine whether the queue is empty.
• IsFull: Determine whether the queue is full.
• Peek: Retrieve a value from the front of the queue without removing it.

Complexity Analysis of Queue Operations

Applications of Queue

• Multi-programming: Multi-programming involves organizing many programs in the main memory as queues.
• Network: Network Queues are utilized in devices such as routers.
• Job Scheduling: The execution of tasks in a predetermined order using queues.
• Synchronization: Data transmission queues between processes (such as IO buffers and pipes).
• Interrupts: Managing in real-time systems.
• Shared resources: Queues are waiting lists for shared resources.
• Data structure operations: Queue utilized in BFS and tree traversal for the input sequence.

Advantages of Queue

• Efficient data processing: Use a queue to process data in the order it is received.
• Resource management: Resource management refers to the queue used to manage shared resources.
• Buffering: A queue for storing incoming data (for example, a network device buffering data packets).
• Memory management: A queue for allocating and releasing memory chunks consecutively.

Disadvantages of Queue

• Limited flexibility: Queues are completely FIFO, with no room for prioritization.
• No random access: Only the first piece is available; the rest must be removed, which limits access efficiency.
• Overhead: Maintaining queue orders incurs costs, particularly for huge lineups.
• Limited size: Some queues are fixed in size, making it difficult to handle big data sets.
• No search operation: Queues lack search functionality and rely only on sequential removal to get elements.