# What Is Queue and Deque in Data Structure?

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Larry Thompson

A queue and deque are important data structures used in computer science and programming. In this article, we will explore what a queue and deque are, their differences, and how they are used in various applications.

## Queue

A queue is a linear data structure that follows the First-In-First-Out (FIFO) principle. Imagine standing in a queue at a supermarket checkout counter – the person who joined the queue first gets served first. Similarly, in a programming context, the element that enters the queue first is the first one to be processed or removed.

In HTML code:

```    `<p>A <b>queue</b> is a linear data structure that follows the First-In-First-Out (FIFO) principle.</p>`
```

### Operations on Queue

• Enqueue: Adds an element to the end of the queue.
• Dequeue: Removes an element from the front of the queue.
• Front: Retrieves the element at the front of the queue without removing it.
• Rear: Retrieves the element at the end of the queue without removing it.
• IsEmpty: Checks if the queue is empty or not.
• IsFull: Checks if the queue is full or has reached its maximum capacity.

The enqueue operation adds elements to the rear end of the queue, while dequeue removes elements from its front end. This ensures that elements are processed in their arrival order, making queues useful for tasks such as handling requests or scheduling processes.

## Deque

A deque, short for double-ended queue, is another linear data structure that allows insertion and deletion of elements from both ends. It combines the features of stacks (LIFO) and queues (FIFO), providing more flexibility in managing elements.

```    `<p>A <b>deque</b>, short for double-ended queue, is another linear data structure that allows insertion and deletion of elements from both ends.</p>`
```

### Operations on Deque

• InsertFront: Adds an element to the front of the deque.
• InsertRear: Adds an element to the rear end of the deque.
• DeleteFront: Removes an element from the front of the deque.
• DeleteRear: Removes an element from the rear end of the deque.
• GetFront: Retrieves the element at the front of the deque without removing it.
• GetRear: Retrieves the element at the rear end of the deque without removing it.
• IsEmpty: Checks if the deque is empty or not.
• IsFull: Checks if the deque is full or has reached its maximum capacity.

The flexibility provided by deques makes them suitable for scenarios where both LIFO and FIFO operations are required. For example, they can be used in algorithms that involve backtracking or in implementing a cache with optimal eviction policies.

## Differences between Queue and Deque

While both a queue and deque are linear data structures, the key difference lies in their flexibility. A queue only supports insertion at one end (rear) and deletion at the other end (front), following the FIFO principle. On the other hand, a deque allows insertion and deletion from both ends, offering more versatility.

```    `<p>While both a <b>queue</b> and <b>deque</b> are linear data structures, the key difference lies in their flexibility.</p>`
```

## Conclusion

Both queues and deques are essential data structures that help manage elements efficiently. Queues follow the FIFO principle, while deques offer more flexibility by allowing insertion and deletion from both ends. Understanding these data structures is crucial for designing optimal algorithms and solving various programming problems.