DoublyLinkedList

/*
 * Enter your code here. Read input from STDIN. Print your output to STDOUT.
 * Your class should be named CandidateCode.
 */

import java.io.*;
import java.util.*;
public class DoublyLinkedList {
    static Node head = null;
    Node tail = null;
    public static void main(String args[] ) throws Exception {
        DoublyLinkedList cd = new DoublyLinkedList();
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int a = sc.nextInt();
        for(int i = 0;i<n;i++) {
            cd.addNode(sc.nextInt());
        }

        cd.display();
        cd.reverse(head);
        cd.display();
    }

    public void display() {
        Node current = head;
        if(head == null) {
            System.out.println("List is empty");
            return;
        }

        while(current != null) {
            //Prints each node by incrementing the pointer.  

            System.out.print(current.data + " ");
            current = current.next;
        }
    }


    Node reverse(Node head) {
        if (head == null || head.next == null) {
            return head;
        }
        Node currNode = head;
        Node prevNode = null;
        while (currNode != null) {
            prevNode = currNode.prev;
            currNode.prev = currNode.next;
            currNode.next = prevNode;
            currNode = currNode.prev;
        }

        head = prevNode.prev;
        return head;
    }



    void addNode(int data) {
        Node newNode = new Node(data);
        if(head == null) {
            head = tail = newNode;
            head.prev = null;
            tail.next = null;
        }
        else {
            tail.next = newNode;
            newNode.prev = tail;
            tail = newNode;
            tail.next = null;
        }
    }
}

class Node{
    int data;
    Node prev;
    Node next;

    public Node(int data) {
        this.data = data;
    }
}