Ques-9.cpp

/*
QUESTION-9:
            Create and perform different operations on Double-ended Queues using Linked List implementation.
SOLUTION:
*/
#include <iostream>
using namespace std;

template <class T>
class node
{
    public:
    T info;
    node *next;

    node(T a,node *p=0)
    {
        info=a;
        next=p;
    }

    ~node()
    {
        delete next;
    }
};

template <class T>
class queue
{
    node <T> *f;
    node <T> *r;
    public:
    queue()
    {
        f=r=0;
    }
    ~queue()
    {
        delete f;
        delete r;
    }

    void Enqueue(T ele);
    T DeQueue();
    void display();
};

template <class T> void queue<T>::Enqueue(T ele)
{
    if(f==0 && r==0)
    {
        r=new node<T>(ele);
        f=r;
    }
    else
    {
        r->next=new node<T>(ele);
        r=r->next;
    }
}

template <class T> T queue<T>::DeQueue()
{
    if(f==0 && r==0)
    {
        cout<<"\nEmpty Stack\n";
        return -99999;
    }
    else
    {
        node <T> *tmp=f;
        f=f->next;
        T d=tmp->info;
        delete tmp;
        return d;
    }
}

template <class T> void queue<T>::display()
{
    if(f==0 && r==0)
    {
        cout<<"\nEmpty Stack\n";
    }
    else
    {
        for(node<T> *p=f;p!=0;p=p->next)
            cout<<p->info<<"\n";
    }
}

int main()
{
    cout << "\n\t ~~~~~~~~~~~~~~~~~~~~~~~Practical 9~~~~~~~~~~~~~~~~~~~~\n\t\t\t\t  \n";
    int ch,n;
    queue <int> q;

    do{
        cout << "\nQueue Using Linked List\n\n 1.Enqueue\n 2.Dequeue\n 3.Display\n 4.Exit\nEnter Your Choice=";
        cin>>ch;

        switch(ch)
        {
            case 1:    cout<<"\nEnter a Number to be Enqueued=";
                    cin>>n;
                    q.Enqueue(n);break;

            case 2:    n=q.DeQueue();
                    if(n!=-99999)
                        cout<<"\nElement Removed="<<n;break;

            case 3:    cout<<"\nElements in the Queue are:-\n";
                    q.display();break;

            case 4:    break;

            default: cout<<"\nInvalid Input.\n";
        }
    }while(ch!=4);

    return 0;
}