void AddToFront(DeqNode node)
{
if (head == null)
{
head = new DeqNode(null);
tail = new DeqNode(null);
head.Next = node;
tail.Next = node;
}
else
{
if (node.Prev != null)
{
node.Prev.Next = null;
}
node.Prev = null;
node.Next = head.Next;
head.Next.Prev = node;
head.Next = node;
}
if (isbnToPosition.ContainsKey(node.Isbn) == false)
{
isbnToPosition.Add(node.Isbn, node);
}
}
void AddToTheFront(string isbn)
{
var node = new DeqNode(isbn);
AddToFront(node);
}
