What Is Queue in a Data Structure?


Angela Bailey

A queue is a fundamental data structure in computer science that follows the concept of “First-In-First-Out” (FIFO). It represents a collection of elements where an element is added to the end (rear) and removed from the front (front). In other words, the element that has been in the queue for the longest time is always at the front, and the newest element is always added to the rear.

Basic Operations on a Queue:

A queue typically supports two main operations:

  • Enqueue: This operation adds an element to the rear of the queue.
  • Dequeue: This operation removes an element from the front of the queue.

Enqueue Operation:

The enqueue operation adds an element to the rear of a queue. When performing this operation, we need to consider two scenarios:

  1. If the queue is empty, we simply add the new element as both the front and rear.
  2. If there are already elements in the queue, we add the new element after the current rear and update it as a new rear.

Dequeue Operation:

The dequeue operation removes and returns an element from the front of a queue. Similar to enqueue, there are two scenarios to consider:

  1. If the queue is empty, there are no elements to remove.
  2. If there are elements in the queue, we remove and return the current front while updating it with its next element.

Real-life Examples of Queues:

The concept of queues can be found in various real-life scenarios. Here are a few examples:

  • Supermarket Checkout: Customers waiting in line to pay at the counter follow a queue. The customer who arrives first is served first, and the customer who arrives last needs to wait until everyone in front of them is served.
  • Print Queue: When multiple print jobs are sent to a printer, they are executed one by one in the order they were received.

    The first job sent is printed first, and subsequent jobs wait their turn in the queue.

  • Call Center Support: Incoming calls are typically handled by call centers using a queue system. The calls are answered by agents in the order they were received, ensuring fairness and efficiency.

Implementing Queues:

In programming, queues can be implemented using various data structures such as arrays or linked lists. Each implementation has its advantages and trade-offs depending on the specific requirements of the problem at hand.

An array-based implementation provides constant-time access to both the front and rear elements but may require resizing if the size exceeds its capacity. On the other hand, a linked list-based implementation allows for dynamic resizing but requires additional memory for maintaining pointers to next elements.

To summarize, queues play an essential role in managing data where maintaining the order of elements is crucial. Understanding how queues work and their basic operations enables developers to efficiently solve problems across various domains.

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