5a6
> 	Node prev;
20c21,23
< 	tail = head;
---
> 	tail = new Node();
> 	head.next = tail;
> 	tail.prev = head;
29,30c32,35
< 	tail.next = tmp;
< 	tail = tmp;
---
> 	tmp.prev = tail.prev;
> 	tmp.next = tail;
> 	tail.prev.next = tmp;
> 	tail.prev = tmp;
36c41
< 	for (Node n = head.next; n != null; n = n.next)
---
> 	for (Node n = head.next; n != tail; n = n.next)
41,46d45
<     private Node findPrev(Object x) {
< 	for (Node p = head; p.next != null; p = p.next)
< 	    if (p.next.item.equals(x))
< 		return p;
< 	return null;
<     }
50,51c49,50
< 	    Node p = findPrev(x);
< 	    p.next = n.next;
---
> 	    n.next.prev = n.prev;
> 	    n.prev.next = n.next;
53,54c52
< 	    if (n == tail)
< 		tail = p;
---
> 	    n.prev = null;
66c64
< 	for (Node n = head.next; n != null; n = n.next)
---
> 	for (Node n = head.next; n != tail; n = n.next)
72c70
< 	for (Node n = head.next; n != null; n = n.next) {
---
> 	for (Node n = head.next; n != tail; n = n.next) {
74c72
< 	    if (n.next != null)
---
> 	    if (n.next != tail)
106c104
< 	    return current != null;
---
> 	    return current != tail;