Queue is a linear list of elements in which deletion of an element can take place at one end, called Front and insertion can take place at the other end, called Rear

The first element in the queue will be the first one to be removed from the list. Queues are also called FIFO(FIRST IN FIRST OUT).

Think of a queue just like a line. It is horizontal. The first one in the line/queue is the first one out. The line starts on the left and ends on the right. Hence you would use pop(), to remove the "last" element of the array.

Applications of the Queue

• Serving request on a single shared resource, eg - PointerEvent, CPU task scheduling, etc,
• In real life, call center phone system(people should wait in and hold until the service representative is free)
• Handling of interrupts in real-time systems.

Basic Operations

The basic operation that can performed are Enqueue, dequeue and display.

Enqueue(terminology for Insertion) - add an item to the queue.

dequeue(terminology for Deletion) - remove an item from the queue

IsEmpty - Checks if the queue is empty.

IsFull - Checks if the queue is full.

Peek - Gets the element at the front of the queue without removing it.

How to use a Queues

Create a queue data structure. The queue should be a class with methods enqueue and dequeue.Adding to the queue should store an element until
it is removed.

Functions to be implemented

enqueue(item) 
dequeue() 
front() 
isEmpty()

Examples Usage

const q = new Queue();
q.enqueue(1);
q.dequeue(); // returns 1;

// Queue class 
class Queue {
  constructor() {
    // Array is used to implement a Queue
    this.data = [];
  }

  // Functions to be implemented 
  // enqueue(item) 
  // dequeue() 
  // front() 
  // isEmpty() 

  // Adds an element to the queue
  enqueue(item) {
    this.data.unshift(item);
  }
  // removing element from the queue 
  // returns underflow when called  
  // on empty queue 

  dequeue() {
    if (this.isEmpty()) {
      return "Underflow";
    }
    return this.data.shift();
  }

  // front function 
  front() {
    // returns the Front element of  
    // the queue without removing it. 
    if (this.isEmpty())
      return "No elements in Queue";
    return this.data[0];
  }

  // isEmpty function 
  isEmpty() {
    // return true if the queue is empty. 
    return this.data.length === 0;
  }
}

module.exports = Queue;

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