queue_using_circular_array.cpp

/*
Queue is a linear data structure which follows FIFO
(First In First Out) Rule. It can be implemented using array/
linked list/ stacks.
*/

#include<bits/stdc++.h>
using namespace std;

//We are creating a class for array
class Queue
{
private:
    int front;
    int rear;
    int capacity;
    int *ptr;

public:

    //Constructor to initialize the data members of Queue class
    Queue(int cap)
    {
        front = 0;
        rear = 0;
        capacity = cap;
        ptr = new int [capacity];
    }

    //Checking if the Queue is empty or not
    bool isEmpty()
    {
        if(front == rear)
            return true;
        return false;
    }

    //Checking if the Queue is full or not
    bool isFull()
    {
        if((rear+1) % capacity == front)
            return true;
        return false;
    }

    //Inserting data into the queue
    void enQueue()
    {
        if(isFull())
            cout<<"\nQueue is Full"<<endl;
        else
        {
            int data;
            cout<<"\nEnter data to be inserted : ";
            cin>>data;
            rear = (rear+1)%capacity;
            ptr[rear] = data;
        }
    }

    //Deleting data from the queue
    void deQueue()
    {
        if(isEmpty())
            cout<<"\nQueue is Empty"<<endl;
        else
        {
            int data;
            front = (front+1)%capacity;
            data = ptr[front];
            cout<<endl<<data<<"  is deleted from Queue"<<endl;
        }
    }

    //Traversing queue and printing data
    void display()
    {
        int i;
        if(rear == front)
            cout<<"\nQueue is Empty"<<endl;
        else
        {
            cout<<"Queue is : ";
            for(i = front+1 ; i != rear ; i = (i+1) % capacity)
                cout<<ptr[i]<<"   ";
            cout<<ptr[rear]<<endl;
        }
    }
};

//Driver Program
int main()
{
    int cap,choice;
    cout<<"Enter the size or capacity of Queue : ";
    cin>>cap;
    Queue q(cap);
    while(1)
    {
        cout<<endl;
        cout<<"1. To enter data into queue."<<endl;
        cout<<"2. To delete data from queue."<<endl;
        cout<<"3. To display the data."<<endl;
        cout<<"4. TO EXIT."<<endl;

        cout<<"\nENTER YOUR CHOICE... : ";
        cin>>choice;

        switch(choice)
        {
        case 1:
            q.enQueue();
            break;

        case 2:
            q.deQueue();
            break;

        case 3:
            q.display();
            break;

        case 4:
            exit(0);
            break;

        default:
            cout<<"\nINVALID CHOICE..."<<endl;
        }
    }
    return 0;
}

/*
    Time Complexities:
    Enqueue --> O(1)
    DeQueue --> O(1)
    IsEmpty --> O(1)
    IsFull  --> O(1)

    Space Complexity: O(n) [for array]
    ----------------------------------
    Sample Input - Output :

    Enter the size or capacity of Queue : 5

    1. To enter data into queue.
    2. To delete data from queue.
    3. To display the data.
    4. TO EXIT.

    ENTER YOUR CHOICE... : 1

    Enter data to be inserted : 10

    1. To enter data into queue.
    2. To delete data from queue.
    3. To display the data.
    4. TO EXIT.

    ENTER YOUR CHOICE... : 1

    Enter data to be inserted : 20

    1. To enter data into queue.
    2. To delete data from queue.
    3. To display the data.
    4. TO EXIT.

    ENTER YOUR CHOICE... : 1

    Enter data to be inserted : 30

    1. To enter data into queue.
    2. To delete data from queue.
    3. To display the data.
    4. TO EXIT.

    ENTER YOUR CHOICE... : 1

    Enter data to be inserted : 40

    1. To enter data into queue.
    2. To delete data from queue.
    3. To display the data.
    4. TO EXIT.

    ENTER YOUR CHOICE... : 3
    Queue is : 10   20   30   40

    1. To enter data into queue.
    2. To delete data from queue.
    3. To display the data.
    4. TO EXIT.

    ENTER YOUR CHOICE... : 2

    10  is deleted from Queue

    1. To enter data into queue.
    2. To delete data from queue.
    3. To display the data.
    4. TO EXIT.

    ENTER YOUR CHOICE... : 1

    Enter data to be inserted : 50

    1. To enter data into queue.
    2. To delete data from queue.
    3. To display the data.
    4. TO EXIT.

    ENTER YOUR CHOICE... : 3
    Queue is : 20   30   40   50

    1. To enter data into queue.
    2. To delete data from queue.
    3. To display the data.
    4. TO EXIT.

    ENTER YOUR CHOICE... : 4

*/