public class LinkedList<E extends Comparable<E>> implements LinkedListInterface<E>
{

    private class Node 
    {
	public E data;
	public Node next;
	public Node(E data, Node next) 
	{
	    this.data = data;
	    this.next = next;
	}	
    }
    
    private Node head = null;
    private Node tail = null;
    private int size = 0;

    @Override
    public int size()
    {
	return size;
    }

    @Override
    public boolean isEmpty()
    {
	return size==0;
    }

    @Override
    public E first()
    {
	if (isEmpty()) 
	{
	    return null;
	}
	else 
	{
	    return (E)head.data;
	}
    }

    @Override
    public E last()
    {
	if (isEmpty()) 
	{
	    return null;
	}
	else 
	{
	    return (E)tail.data;
	}
}

    @Override
    public void addLast(E e)
    {
	Node newest = new Node(e, null);
	if (isEmpty()) 
	{ 
	    head = newest;
	}
	else 
	{
	    tail.next=newest;
	}
	tail = newest; 
	size++;  
	
    }

    @Override
    public void addFirst(E e)
    {
	Node newest = new Node(e, null);
	if (isEmpty())
	{
	    tail=newest;
	}
	else
	{
	    newest.next=head;
	}
	head=newest;
	size++;
	
    }

    @Override
    public E removeFirst()
    {
	if (isEmpty()) {return null;}
	E target = (E)head.data;
	head = head.next; 
	size--;
	if (isEmpty()) {tail = null;}
	return target;
    }

    @Override
    public E removeLast()
    {
	if (isEmpty()) return null;
	if (head==tail)
	{
	    E target=(E)head.data;
	    head=null;
	    tail=null;
	    size=0;
	    return target;
	}
	Node prev = null;
	for (Node n=head; n!=tail; n=n.next)
	{
	    prev=n;
	}
	prev.next=null;
	E target = (E)tail.data;
	tail=prev;
	size--;
	return target;
    }

    @Override
    public E remove(E e)
    {
	if (isEmpty()) {return null;}
	Node prev=null;
	Node current = head;
	while (current !=null && current.data != e)
	{
	    prev=current;
	    current = current.next;
	}
	if (current==null)
	{
	    return null;
	}
	if (current==tail)
	{
	    tail=prev;
	}
	if (current==head)
	{
	    return removeFirst();
	}
	prev.next=current.next;
	size--;
	if (size==0)
	{
	    head=null;
	    tail=null;
	}
	return e;

    }

    @Override
    public E find(E e)
    {
	Node curr = head;
	while (curr!=null)
	{
	    if (curr.data.compareTo(e)==0)
	    {
		return (E)curr.data;
	    }
	    curr=curr.next;
	}
	return null;

    }
    
    public String toString() {
   	StringBuffer s = new StringBuffer();
   	for (Node n=head; n!=null; n=n.next)
   	{
   	    s.append( n.data.toString());
   	    if (n != tail) 
   	    {
   	        s.append("\n");
   	    }
   	}
   	return s.toString();
       }


}