Doubly Queue ISC Computer Science 2013 Theory

A doubly queue is a linear data structure which enables the user to add and remove integers from either ends, i.e. from front or rear. Define a class Dequeue with the following details:

Class name: Dequeue

Data members/instance variables:
arr[]: array to hold up to 100 integer elements
lim: stores the limit of the dequeue
front: to point to the index of front end
rear: to point to the index of the rear end

Member functions:
Dequeue(int l): constructor to initialize the data members lim = l, front = rear = 0
void addFront(int val): to add integer from the front if possible else display the message "Overflow from front"
void addRear(int val): to add integer from the rear if possible else display the message "Overflow from rear"
int popFront(): returns element from front, if possible otherwise returns -9999
int popRear(): returns element from rear, if possible otherwise returns -9999

Specify the class Dequeue giving details of the constructor, void addFront(int), void addRear(int), int popFront() and int popRear(). The main() function and algorithm need not be written.

import java.util.Scanner;
class Dequeue{
    int arr[];
    int lim;
    int front;
    int rear;
    public Dequeue(int l){
        lim = l;
        if(lim > 100)
            lim = 100;
        arr = new int[100];
        front = 0;
        rear = 0;
    }
    public void addFront(int val){
        if(front == 0)
            System.out.println("Overflow from front");
        else
            arr[--front] = val;
    }
    public void addRear(int val){
        if(rear == lim)
            System.out.println("Overflow from rear");
        else
            arr[rear++] = val;
    }
    public int popFront(){
        if(front < rear){
            int d = arr[front++];
            if(front == rear){
                front = 0;
                rear = 0;
            }
            return d;
        }
        return -9999;
    }
    public int popRear(){
        if(front < rear){
            int d = arr[--rear];
            if(front == rear){
                front = 0;
                rear = 0;
            }
            return d;
        }
        return -9999;
    }
    public static void main(String[] args){
        Scanner in = new Scanner(System.in);
        System.out.print("Dequeue limit: ");
        int limit = Integer.parseInt(in.nextLine());
        Dequeue dq = new Dequeue(limit);
        while(true){
            System.out.println("1. Add from front");
            System.out.println("2. Add from rear");
            System.out.println("3. Pop from front");
            System.out.println("4. Pop from rear");
            System.out.print("Enter your choice: ");
            int choice = Integer.parseInt(in.nextLine());
            switch(choice){
            case 1:
                System.out.print("Element to be added: ");
                int v = Integer.parseInt(in.nextLine());
                dq.addFront(v);
                break;
            case 2:
                System.out.print("Element to be added: ");
                v = Integer.parseInt(in.nextLine());
                dq.addRear(v);
                break;
            case 3:
                v = dq.popFront();
                if(v == -9999)
                    System.out.println("Underflow from front");
                else
                    System.out.println(v + " popped");
                break;
            case 4:
                v = dq.popRear();
                if(v == -9999)
                    System.out.println("Underflow from rear");
                else
                    System.out.println(v + " popped");
                break;
            default:
                System.out.println("Bye!");
                return;
            }
        }
    }
}