CS 61B Lab 4
                             February 13-14, 2014

Goal:  This lab will demonstrate how a sentinel node can simplify a
doubly-linked list implementation.

Copy the Lab 4 directory by starting from your home directory and typing:

  cp -r ~cs61b/lab/lab4 .
  cd lab4

Getting Started
---------------
Please make sure you have a partner for this lab.

The files in the lab4 directory contain classes for two different types of
doubly-linked list.  The DList1 class does not use a sentinel, whereas the
DList2 class does.  The DList1 class is not circularly linked, but the DList2
class is (through the sentinel).  Compile DList1.java and DList2.java (using
"javac -g DList1.java DList2.java".)

Your task is to implement two insertFront() and two removeFront() methods--one
of each for each list class.  insertFront() and removeFront() insert or remove
an item at the beginning of a list.  Make sure your implementations work for
empty lists, one-node lists, and larger lists.

The main() methods of DList1 and DList2 include test code, which you can run
with "java DList1" and "java DList2".

Part I:  insertFront in DList1 (1 point)
----------------------------------------
Write a method called DList1.insertFront() that inserts an int at the front of
"this" DList1.

Part II:  removeFront in DList1 (1 point)
-----------------------------------------
Write a method called DList1.removeFront() that removes the first item (and
node) from "this" DList1.

Part III:  insertFront in DList2 (1 point)
------------------------------------------
Write a method called DList2.insertFront() that inserts an int at the front of
"this" DList2.  Your code should NOT use any "if" statements or conditionals.

Part IV:  removeFront in DList2 (2 points)
------------------------------------------
Write a method called DList2.removeFront() that removes the first item (and
non-sentinel node) from "this" DList2.  Your code should not require separate
branches for the one-node case and the more-than-one-node case.  (You will
need one "if", to handle the zero-node case.)

Check-off
---------
Run the DList1 and DList2 test code for your TA or Lab Assistant.

1 point:  DList1.insertFront().
1 point:  DList1.removeFront().
1 point:  DList2.insertFront().
1 point:  DList2.removeFront().