Queue - DSA | Part 6 |

A queue is a useful data structure in programming. It is similar to the ticket queue outside a cinema hall, where the first person entering the queue is the first person who gets the ticket.

Queue follows the First In First Out (FIFO) rule - the item that goes in first is the item that comes out first.

In programming terms, putting items in the queue is called enqueue, and removing items from the queue is called dequeue.

Basic Operations of Queue

A queue is an object (an abstract data structure - ADT) that allows the following operations:

Enqueue: Add an element to the end of the queue
Dequeue: Remove an element from the front of the queue
IsEmpty: Check if the queue is empty
IsFull: Check if the queue is full
Peek: Get the value of the front of the queue without removing it

Queue Implementations in C++

#include <iostream>
#define SIZE 5

using namespace std;

class Queue {
   private:
  int items[SIZE], front, rear;

   public:
  Queue() {
    front = -1;
    rear = -1;
  }

  bool isFull() {
    if (front == 0 && rear == SIZE - 1) {
      return true;
    }
    return false;
  }

  bool isEmpty() {
    if (front == -1)
      return true;
    else
      return false;
  }

  void enQueue(int element) {
    if (isFull()) {
      cout << "Queue is full";
    } else {
      if (front == -1) front = 0;
      rear++;
      items[rear] = element;
      cout << endl
         << "Inserted " << element << endl;
    }
  }

  int deQueue() {
    int element;
    if (isEmpty()) {
      cout << "Queue is empty" << endl;
      return (-1);
    } else {
      element = items[front];
      if (front >= rear) {
        front = -1;
        rear = -1;
      } 
      else {
        front++;
      }
      cout << endl
         << "Deleted -> " << element << endl;
      return (element);
    }
  }

  void display() {
    int i;
    if (isEmpty()) {
      cout << endl
         << "Empty Queue" << endl;
    } else {
      cout << endl
         << "Front index-> " << front;
      cout << endl
         << "Items -> ";
      for (i = front; i <= rear; i++)
        cout << items[i] << "  ";
      cout << endl
         << "Rear index-> " << rear << endl;
    }
  }
};

int main() {
  Queue q;


  q.deQueue();


  q.enQueue(1);
  q.enQueue(2);
  q.enQueue(3);
  q.enQueue(4);
  q.enQueue(5);


  q.enQueue(6);

  q.display();


  q.deQueue();


  q.display();

  return 0;
}

Blog

Queue - DSA | Part 6 |

Madhuban Khatri

Basic Operations of Queue

Queue Implementations in C++

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