# Queue Data Structure: Types, Implementation, Applications

*A queue is a linear data structure that stores the elements sequentially. It uses the FIFO (First In First Out) approach for accessing elements. Queues are typically used to manage threads in multithreading and implementing priority queuing systems. In this article, we will learn about different types of queue data structures, basic operations performed on them, implementation, and queue applications.*

A **queue **is an important data structure in **programming**. A queue follows the FIFO (First In First Out) method and is open at both of its ends. Data insertion is done at one end, the rear end or the tail of the queue, while deletion is done at the other end, called the front end or the head of the queue.

### Real Life Queue in Data Structure Example

Let’s consider a queue in data structure example. A line of people is waiting to buy a ticket at a cinema hall. A new person will join the line from the end, and the person standing at the front will be the first to get the ticket and leave the line. Similarly in a queue data structure, data added first will leave the queue first.

Some other applications of the queue in real-life are:

- People on an escalator
- Cashier line in a store
- A car wash line
- One way exits

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## Types of Queues in Data Structure

There are four different types of queues in data structures:

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**Simple Queue**

Simple Queue is a linear data structure that follows the First-In-First-Out (FIFO) principle, where elements are added to the rear (back) and removed from the front (head).

- Ordered collection of comparable data kinds.
- Queue structure is FIFO (First in, First Out).
- When a new element is added, all elements added before the new element must be deleted in order to remove the new element.

**Circular Queue**

A circular queue is a special case of a simple queue in which the last member is linked to the first. As a result, a circle-like structure is formed.

- The last node is connected to the first node.
- Also known as a
**Ring Buffer,**the nodes are connected end to end. - Insertion takes place at the front of the queue, and deletion at the end of the queue.
**Circular queue application:**Insertion of days in a week.

**Priority Queue**

In a priority queue, the nodes will have some predefined priority in the priority queue. The node with the least priority will be the first to be removed from the queue. Insertion takes place in the order of arrival of the nodes.

Some of the applications of priority queue:

- Dijkstra’s shortest path algorithm
- Prim’s algorithm
- Data compression techniques like Huffman code

Below diagram shows how an application use priority queue for the items consumed by the user.

**Deque (Double Ended Queue)**

In a double-ended queue, insertion and deletion can occur at both the queue's front and rear ends.

## Basic Queue Operations in Queue Data Structure

Below are the basic queue operations in data structure:

Operation |
Description |
---|---|

enqueue() |
Process of adding or storing an element to the end of the queue |

dequeue() |
Process of removing or accessing an element from the front of the queue |

peek() |
Used to get the element at the front of the queue without removing it |

initialize() |
Creates an empty queue |

isfull() |
Checks if the queue is full |

isempty() |
Check if the queue is empty |

Now, let us understand in detail the two primary operations associated with Queue data structure – enqueue and dequeue.

### Enqueue Operation

Below are the steps to enqueue (insert) data into a queue

- Check whether the queue is full or not.
- If the queue is full – print the overflow error and exit the program.
- If the queue is not full – increment the rear pointer to point to the next empty space.
- Else add the element in the position pointed by Rear.
- Return success.

**Algorithm for Enqueue Operation**

procedure enqueuer (data) if queue is full
return overflow endif
rear ← rear + 1 queue[rear] ← data
return true end procedure

### Dequeue Operation

Below are the steps to perform the dequeue operation

- Check whether the queue is full or not.
- If the queue is empty – print the underflow error and exit the program.
- If the queue is not empty – access the data where the front is pointing.
- Else increment the front pointer to point to the next available data element.
- Return success.

**Algorithm for Dequeue Operation**

procedure dequeue if queue is empty
return underflow end if data = queue[front]front ← front + 1return trueend procedure

## Implementation of Queue

**A queue can be implemented in two ways: **

- Sequential allocation: It can be implemented using an
**array**. A queue implemented using an array can organize only a limited number of elements. - Linked list allocation: It can be implemented using a
**linked list**. A queue implemented using a linked list can organize unlimited elements.

Now, let’s move on to the application of queue.

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## Queue applications in Data Structure

A queue data structure is generally used in scenarios where the FIFO approach (First In First Out) has to be implemented. The following are some of the most common queue applications in data structure:

- Managing requests on a single shared resource such as CPU scheduling and disk scheduling
- Handling hardware or real-time systems interrupts
- Handling website traffic
- Routers and switches in networking
- Maintaining the playlist in media players

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## Conclusion

We hope you found this article useful. Gaining a solid understanding of the important concept of queue data structure, its types, implementation, and applications will help you to improve your skills to work on projects that require knowledge of queue data structures.

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## FAQs

**With what data structure can a priority queue be implemented?**

A priority queue can be implemented using a variety of data structures, such as a linked list, array, binary search tree, or heap. However, the heap is the most efficient data structure to implement a priority queue.

**What is the queue data structure used for?**

The queue data structure has a variety of applications. The queue data structure is used for serving requests on a single shared resource, i.e. when a single resource is shared among multiple consumers, such as printer and CPU task scheduling. The queue data structure is also used for managing the hardware or real-time systems interrupts, managing website traffic, and routers and switches in networks.

**What is the difference between stack and queue in data structure?**

The stack and queue are the linear data structures, in which the elements are stored sequentially and accessed in a single run. The main difference between stack and queue in data structure is that stack follows the LIFO principle whereas Queue follows the FIFO approach. In LIFO or Last In First Out, the last element inserted in the stack will be processed first while in FIFO or First In First Out, the first element in a queue will be processed first.

**What is a double ended queue in data structure?**

A double ended queue is a kind of queue data structure in which insertion and removal of elements can take place at both ends, i.e. front and back.

**Does queue follow a FIFO or LIFO principle?**

A queue data structure follows a FIFO (first in first out) data structure. In FIFO, the first element added to the queue will be removed first. LIFO (last in first out) is used by stack data structure.

**How can I implement Queue Data structure?**

You can either use arrays or linked Lists to represent and implement Queues in any programming language.

**About the Author**

Rashmi is a postgraduate in Biotechnology with a flair for research-oriented work and has an experience of over 13 years in content creation and social media handling. She has a diversified writing portfolio and aim... Read Full Bio

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