// removes the element at the beginning of the collection
public T RemoveFirst()
{
if (first == null) // 0 items
{
throw new InvalidOperationException("Linked list empty!");
}
T currentFirstValue = first.Value;
if (first == last) // 1 item
{
first = null;
last = null;
}
else // more than 1 item
{
LinkedListItem <T> newFirst = first.Next;
newFirst.Previous = null;
first = newFirst;
}
return(currentFirstValue);
}
// removes the element at the end of the collection
public T RemoveLast()
{
if (last == null)
{
throw new InvalidOperationException("Linked list empty!");
}
T currentLastValue = last.Value;
if (first == last)
{
first = null;
last = null;
}
else
{
LinkedListItem <T> newLast = last.Previous;
newLast.Next = null;
last = newLast;
}
return(currentLastValue);
}