//Garth Bruen
//10.09.02


/*
	Set up with extra statements and methods to
	show the backlinking in action
*/


public class LL21{


	private Node head;
	private Node next;
	private Node previous;

	class Node{
		int data;
		Node next = null;
		Node previous = null;
	}//end Node()


	public void addTo(int data){

		Node newNode = new Node();
		newNode.previous = null;		
		newNode.data = data;
		newNode.next = head;
		head = newNode;

	}//end addFirst()

	public Node backlink(){

		Node current = head; //Begining of list
		Node prev = null; //temp node

		while(current.next != null){
			prev = current;
			current = current.next;
			System.out.println("current is: "+current.data);
			if(current != null){
			current.previous = prev;
			System.out.println("prev is: "+current.previous.data);
			}
		}

		this.printList(); 

	return current;
	}//end

	public void printList(){
		Node current = head;
		while(current != null){
			System.out.print(current.data);
			if(current.previous != null){
				System.out.print(current.previous.data);
			}
			current = current.next;

		}
		
		System.out.println();

	}//end printList()
	

	public static void main(String args[]) throws Exception
	{
		LL21 unsorted = new LL21();
		unsorted.addTo(1);
		unsorted.addTo(2);
		unsorted.addTo(3);
		unsorted.addTo(4);
		unsorted.addTo(5);
		unsorted.addTo(6);
		unsorted.addTo(7);
		unsorted.addTo(8);
		unsorted.addTo(9);
		unsorted.printList();
		unsorted.backlink();
		
		
		
	}//End main
}