CSCI 136

CSCI 136 - Spring 2018

Data Structures & Advanced Programming

Lab 9: Hex-a-Pawn

This week you may again choose to work with a partner. This is a challenging lab because it can be hard to debug. Discussing your design with a parnter will be helpful! If you would like to work by yourself, we still encourage you to collaborate with a "discussion partner" in lab to finalize your design—you can still independently code and submit your lab after an initial strategy discussion. Debugging your design will help you to write bug-free code!

This week's lab uses trees to play Hex-a-Pawn, a small chess-like game. The lab is outlined in Section 12.11 of your textbook. You will build a tree that starts from the initial game state and represents all possible game board states. You will then implement several different players that consult this tree to make moves as they play Hex-a-Pawn. The players include:
  1) a human player that asks the user for moves to make
  2) a random player that picks possible moves at random
  3) a computer player that improves its strategy by learning from past mistakes.

In the end, you will be able to run the different players against each other.

Pre-lab

Before arriving to your scheduled lab, prepare a design document for the GameTree class. It will not be collected, but it will be worth 2 points of your lab grade. For those who choose to work with a partner, each partner must prepare their own design document; you should collaborate on a final design after the lab has started.

There are three starter files available on the lab page: HexBoard.java (javadoc), HexMove.java (javadoc),, and Player.java (javadoc). Familiarize yourself with these classes. They are described briefly in the book, and the javadoc documentation should be a helpful reference.

Regardless of whether or not you would like to work with a partner, please fill out the following online form by Tuesday at 5pm so that we can make your Lab 8 repositories.

Lab Details

The lab is described in Section 12.11 of your textbook. The description below is meant to supplement the instructions there, so carefully read the lab description in the textbook first.

A significant part of your task is to design and implement the GameTree class. This is a tree structure with potentially many children instead of just two. Think about the methods you will need in this class and how you can represent the structure as you construct your design document.
After finishing your GameTree constuctor, you may want to implement a size() method to verify that you have created the proper number of GameTree nodes. You can think of your size() the same way we implemented size() for a linked list: count yourself, then add the size() of each of your children to a running total.
You can play a game of Hex-a-Pawn by running
```
	  $ java HexBoard
	
```
after compiling the starter files. Look at the HexBoard code: it allows you to play a complete game, so its implementation may be insightful!
To use your three Player classes as described in the book, implement the Hex-a-Pawn game as the main method of a class HexaPawn.java. This program should take four command-line arguments (i.e., arguments specified in args[]). The first two arguments specify the number of rows and columns the board should have. The third and fourth arguments should be the string "human", "comp", or "random" to indicate what type of player should be used for the white and black pieces, respectively. Remember that you can convert a String to an integer with the Integer.parseInt(str) method.
The CompPlayer should "trim its tree" when it loses: it should remove the single GameTree node that represents a losing move. Your CompPlayer class may need to keep track of some extra state so that your CompPlayer's play method doesn't trim more than one GameTree node per loss.
Gardner's original paper describing this game can be found at GardnerHexapawn.pdf (only visible from campus). Take a look, if you're interested. Notice the ad for a "comparator" on the third page!

Thought Questions

Please answers thought questions 1 and 2 from the book (pg 314). When working on the thought problems, your program may run out of memory. You may increase the size of the heap for your program by running it as, for example:

	  $ java -Xmx500m HexaPawn 3 3 comp human

The option "-Xmx500m" indicates that your program is allowed to allocate up to 500MiB of memory using the new keyword.

Lab Deliverables

Please complete and submit the following items in your repository:

Your well-documented source code for all Java files that you write (GameTree.java, HumanPlayer.java, RandomPlayer.java, CompPlayer.java, and HexaPawn.java).
Answers to thought questions 1 and 2 from the book (pg 314) in a file called PROBLEMS.md.

Submitting Your Lab

As you complete various milestones, you should commit your changes and push them. Commit early and often. When the deadline arrives, we will retrieve the latest version of your code. If you are confident that you are done, please include "Lab Submission" as the commit message for your final commit. If you later decide that you have more edits to make, it is OK. We will look at the latest commit before the deadline.

Be sure to push your changes to GitHub
Verify your changes on Github. Navigate in your web browser to your team's private repository on GitHub. It should be available at:
```
https://github.com/williams-cs/cs136lab9-{USERNAME1-USERNAME2}
```
You should see all changes reflected in the various files that you submit. If not, go back and make sure you committed and pushed.

We will know that the files are yours because they are in your git repository. Do not include identifying information in the code that you submit. Our goal is to grade the programs anonymously to avoid any bias. However, in your README.md file, please cite any sources of inspiration or collaboration (e.g., conversations with classmates). We take the honor code very seriously, and so should you. Please include the statement "I am the sole author of the work in this repository." in the comments at the top your java files.