/**
 *
 * Ashish Patel
 * e: ashishsushilPatel@gmail.com
 * w: https://ashish.me
 *
 */

class ReverseDoublyList {

  static DoublyNode reverseList(DoublyNode head) {
    if (head == null) {
      return null;
    }
    DoublyNode temp = null;
    DoublyNode current = head;
    while(current != null){
      temp = current.prev;
      current.prev = current.next;
      current.next = temp;
      current = current.prev;
    }
    return temp.prev;
  }

  public static void main(String[] args) {
    DoublyNode head = new DoublyNode(10);
    DoublyNode temp1 = new DoublyNode(20);
    DoublyNode temp2 = new DoublyNode(30);
    head.next = temp1;
    temp1.prev = head;
    temp1.next = temp2;
    temp2.prev = temp1;
    head = reverseList(head);
    printlist(head);
  }

  public static void printlist(DoublyNode head) {
    DoublyNode curr = head;
    while (curr != null) {
      System.out.print(curr.data + " ");
      curr = curr.next;
    }
    System.out.println();
  }
}