Homework #2: Game Playing
Specification Due: October 10th
Full Program Due: October 19th, 2006
 

Programs and specifications are due at the beginning of class on the due date.

You may work in teams of two on this assignment if you like. If you work in a team of two, you must allow for four person play.

For this assignment you are to write a program that can play Pente. You can make the following assumptions.

1.  You are playing against one other opponent (if you are doing the assignment alone) or an option for two or four players if you working as part of a pair.
2.  Your opponent can be either a human or a computer

How to play Pente: You are given a Pente board consisting of a grid of 19X19 lines, plus two sets of stones. You can assume an endless supply of stones. The first player (chosen by chance) begins the game by playing one stone on the center point. Thereafter, the players take turns playing their stones, one at a time, on any empty intersection. There is one restriction: on the second turn, the first player's move must not be within 2 spaces of the piece on the center. The stones are played on the intersections of the lines (including the edge of the board), rather than in the squares. Once played, a stone cannot be moved again (except when removed by a capture as explained below).

The game is won by the first player to play five in a row or to capture 5 pairs from the opponent.

When four players play, there are four colors, one per player. The players split up into two teams. Team members sit opposite each other. The first player moves on the center point. Thereafter the players take turns, in a clockwise direction, placing their stones on the intersectsions of the lines as in basic Pente. Each player controls a different color of stones, and cooperates with his or her partner for a team win. If you working in a pair, you need to implement both two player and four player games. You can start by implementing the four player game without teams and then add in teams (i.e., it would be easier to start thinking about it without teams).

The full set of rules are provided at the two websites below. The first has a little better explanation, but is lacking the restrictions on the first player. The second states those restrictions.

Strategy. There is some strategy to playing Pente. Two of the web sites below have more information on strategy, but at the basic level keep in mind the following tips: The best strategy for winning at Pente is to try to seize the offensive. The person who is on the offensive is able to exercise more control over the game's direction, and therefore over its final outcome. Basically one gets on the offensive by making stronger moves than one's opponent, which usually means having more stones in a row so that he or she has to block your rows and not vice versa. You will find that "threes" are the basic building blocks of threats in Pente and come in a variety of shapes. Use them to gain the initiative by quickly developing a series of intersecting threes and fours and extending them in all directions. Keep moving to give oneself as many options for further play as possible, placing the stones so that they build upone each other, until an unstoppable "double threat" is achieved. When looking for good moves consider those that seem like they might come naturally. Moves that give the position balance or symmetry often work very well, as do moves that are visually striking or appealing. Often the point where the opponent would like to play next is also the best place for one's own stone.

Websites:
     Rules of Pente and links to strategies, but without restrictions on first player  
     Rules of Pente, with restrictions on first player.    
     Lots of information on Pente,   (you can download a demo version of  the game. Source code is available here but you will not do well if you copy in any way.)


Implementation: You are to implement a minimax search using alpha-beta pruning. You should set up your program so that search depth can be a user provided parameter and you can run your program with different levels of lookahead. You should implement an evaluation function that estimates how good a particular game state is. You should consider strategies, such as the ones given on the web sites, when implementing your evaluation function. You will be graded in part on the creativity you show in implementing your evaluation function. In your program, you will need to keep track of the state space, which should include the layout of the board and the number of pairs that each player has captured. You will also need to keep track of stones in a row; when you make a move that results in 5 stones in a row or 5 captured pairs, your program should declare that you are the winner. Finally, if you make an illegal move, then you lose the game.

In order to limit your search space, at each turn, consider the moves that are within 5 spaces in any direction of the pieces on the board. You should not consider every possible space on the board.

Specifications: In order to ensure that you don't wait until the last week to begin writing your program (in which case you will most certainly not finish in time), you must turn in a specification for your program by Oct. 10th. This should include: 1. the algorithm for alpha beta cut-offs, 2. a description of the evaluation function that you plan to use (which should include at least three features) and an algorithm that computes the values for each feature, and 3. the algorithm for your move generator. In addition, you should provide two paragraphs of text that describe your approach. All algorithms should be provided in pseudo code. The specification that you provide will count for 15% of your grade.

What to turn in: For this assignment, you will use the online submission to turn in the code and a readme file. All code should be well documented. You will be graded in part based on this documentation. You will bring hard copy of the readme file to class. You do not need to turn in hardcopy of your code. The readme file should include: 1. A description of your approach and any special points that you think we should know about, 2. A short paragraph explaining how you did each of the following requirements and the name of the class that implements it in your program: minimax search, alpha-beta pruning, move generator, evaluation function, score computation. If you are working in a pair, your readme file should describe what each person of the team did and you should clearly identify who did each piece of code. You can also describe parts that you did jointly.

You will be provided with a module which will actually perform the move that your program decides to make and update the state space.

• Download the package here: assignment2.tar.gz.
• Documentation for compiling and running the assignment is accessible in the coms4701-docs directory. To read the instructions, open "index.html", then click on the link for the package "agent.environments.pente", which is labeled as Assignment 2.

There will be a tournament following the due date which is optional. Everyone entering the tournament will receive 10 points of extra credit and there will be a series of extra credits for teams that win at each round.