Build Both Ends of a Deque

A deque has four doors: add and remove at each end. Lock two of them and the same class becomes something familiar - addFirst with removeFirst is a stack, addLast with removeFirst is a queue. LinkedDeque already gives you isEmpty, size and toString; write the four operations.

Requirements:
1. addFirst(int value) and addLast(int value) link a new DNode at that end and grow the size.
2. removeFirst() and removeLast() unlink that end and return its value, or return -1 when the deque is empty.
3. head, tail and size must stay in agreement, so a deque drained to empty can be filled again from either end.

The DNode class is provided - do not rename it and do not add public to it, because a Java source file may contain only one public class.

Do NOT write a main method.