Tuesday, July 28, 2009

A Checkers Rules Engine in C#

One of the things I've always wanted to program is a game using a Genetic Algorithm to generate the AI. Well at work I was talking about AI coding and my aforementioned desire came up and as we talked about it, the idea of using game of Checkers as the game I could use with a GA surfaced.

When I got home that evening and was relaxing after diner, I booted up the laptop and started cruising around the web. I was started looking around for a rules engine for checkers - hopefully in C#. You see my thought was, if I could find a rules engine that, from a given game board configuration and who's move it was, it would output all valid moves.

Well, no matter how I arranged the words in Google, I could not find a rules engine for checkers. I found a few complete C# checkers games but the rules were too integrated into the rest of the game for me to filter out.

So, I decided to write one.

I started with an enum to define the two players:
public enum PlayerColors { Black, Red }

Then I wrote a class to hold each checker piece:

CheckerPiece has a single constructor:
CheckerPiece(PlayerColors MyPlayerColor, int MyPieceLocation, bool MyIsKing)

Four properties:
public int PieceLocation { get; set; }
public bool IsKing { get; set; }
public PlayerColors PlayerColor { get; set; }
public List PossibleMoveLocations { get; set; }

and Three methods:
public char GetPlayCharacter()
public void FindAllMoves(char[] GameboardArray)
public void FindAllJumps(char[] GameboardArray)

The constructor sets the PlayerColor, PieceLocation, and IsKing.

PlayerColor defines which side the piece belongs to.
PieceLocation is an int from 0 to 63 defining each square of the game board.
IsKing is a bool that determines if the piece is a king or not.

GetPlayCharacter returns a lowercase r for a red piece, a lowercase b for a black piece, an uppercase R for a red king piece and an uppercase B for a black king piece.

a game board array is a char[64] array that can hold on of these chars 'r', 'R', 'b', 'B' or ' ' (a space).

FindAllMoves and FindAlJumps take in a GameboardArray and sets the PossibleMoveLocations list with all the possible Moves or Jumps.

Now with that built, I created the CheckersRulesEngine class.

CheckersRulesEngine has a single constructor:
public CheckersRulesEngine(char[] gameboardarray)

A static char array that holds a starting game board configuration for convenience:
static public readonly char[] StartingGameboardArray =
" b b b bb b b b b b b b r r r r r r r rr r r r ".ToCharArray();

Three properties:
public List MovablePieces { get; set; }
public List Pieces { get; set; }
public char[] GameboardArray { get; set; }

And Three Methods:
public void GetPiecesWithMoves(PlayerColors CurrentPlayer)
public void GetPiecesWithJumps(PlayerColors CurrentPlayer)
public string OutputAsciiBoard()

The constructor the GameboardArray and creates a CheckerPiece entry into Pieces for each piece defined in the GameboardArray.

GetPiecesWithMoves and GetPiecesWithJumps works its way through the Pieces collection and loads MovablePieces with the pieces that qualify.

OutputAsciiBoard is a helper function that outputs an ascii board showing the location of all the pieces.

You can get the c# code for the CheckersRulesEngine here! Or, you can download a Visual Studio 2008 solution that also includes a console program that plays a game of checkers against itself using random moves! The solution can be downloaded Here!


Unknown said...

good work, but it would b much better if there was a AI or GA approach

Anonymous said...

I love it! thanks!