I'm making a version of Martian Chess in java with AI and so far I THINK my move searching is semi-working, it seems to work alright for some depths but if I use a depth of 3 it returns a move for
the opposite side...now
the game is a bit weird because when a piece crosses half of
the board, it becomes property of
the other player so I think this is part of
the problem. I'd be really greatful if someone could look over my code and point out any errors you think are there! (pls note that my evaluation function isn't nearly complete lol)
MoveSearch.java
public class MoveSearch {
private Evaluation evaluate = new Evaluation();
private int blackPlayerScore, whitePlayerScore;
public MoveContent bestMove;
public MoveSearch(int blackScore, int whiteScore) {
blackPlayerScore = blackScore;
whitePlayerScore = whiteScore;
}
private Vector<Position> EvaluateMoves(Board board) {
Vector<Position> positions = new Vector<Position>();
for (int i = 0; i < 32; i++) {
Piece piece = null;
if (!board.chessBoard[i].square.isEmpty()) {
// store
the piece
piece = board.chessBoard[i].square.firstElement();
}
// skip empty squares
if (piece == null) {
continue;
}
// skip
the other players pieces
if (piece.pieceColour != board.whosMove) {
continue;
}
// generate valid moves for
the piece
PieceValidMoves validMoves = new PieceValidMoves(board.chessBoard, i, board.whosMove);
validMoves.generateMoves();
// for each valid move
for (int j = 0; j < piece.validMoves.size(); j++) {
// store it as a
position
Position move = new Position();
move.startPosition = i;
move.endPosition = piece.validMoves.elementAt(j);
Piece pieceAttacked = null;
if (!board.chessBoard[move.endPosition].square.isEmpty()) {
// if
the end
position is not empty, store
the attacked piece
pieceAttacked = board.chessBoard[move.endPosition].square.firstElement();
}
// if a piece is attacked
if (pieceAttacked != null) {
// append its value to
the move score
move.score += pieceAttacked.pieceValue;
// if
the moving pieces value is less than
the value of
the attacked piece
if (piece.pieceValue < pieceAttacked.pieceValue) {
// score extra points
move.score += pieceAttacked.pieceValue - piece.pieceValue;
}
}
// add
the move to
the set of positions
positions.add(move);
}
}
return positions;
} // EvaluateMoves()
private int SideToMoveScore(int score, PieceColour colour) {
if (colour == PieceColour.Black){
return -score;
} else {
return score;
}
}
public int AlphaBeta(Board board, int depth, int alpha, int beta) {
//int best = -9999;
// if
the depth is 0, return
the score of
the current board
if (depth <= 0) {
board.printBoard();
System.out.println("Score: " + evaluate.EvaluateBoardScore(board));
System.out.println("");
int boardScore = evaluate.EvaluateBoardScore(board);
return SideToMoveScore(boardScore, board.whosMove);
}
// fill
the positions with valid moves
Vector<Position> positions = EvaluateMoves(board);
// if there are no available positions
if (positions.size() == 0) {
// and its blacks move
if (board.whosMove == PieceColour.Black) {
if (blackPlayerScore > whitePlayerScore) {
// and they are winning, return a high number
return 9999;
} else if (whitePlayerScore == blackPlayerScore) {
// if its a draw, lower number
return 500;
} else {
// if they are losing, return a very low number
return -9999;
}
}
if (board.whosMove == PieceColour.White) {
if (whitePlayerScore > blackPlayerScore) {
return 9999;
} else if (blackPlayerScore == whitePlayerScore) {
return 500;
} else {
return -9999;
}
}
}
// for each
position
for (int i = 0; i < positions.size(); i++) {
// store
the position
Position move = positions.elementAt(i);
// temporarily copy
the board
Board temp = board.copyBoard(board);
// make
the move
temp.makeMove(move.startPosition, move.endPosition);
for (int x = 0; x < 32; x++) {
if (!temp.chessBoard[x].square.isEmpty()) {
PieceValidMoves validMoves = new PieceValidMoves(temp.chessBoard, x, temp.whosMove);
validMoves.generateMoves();
}
}
// repeat
the process recursively, decrementing
the depth
int val = -AlphaBeta(temp, depth - 1, -beta, -alpha);
// if
the value returned is better than
the current best score, replace it
if (val >= beta) {
// beta cut-off
return beta;
}
if (val > alpha) {
alpha = val;
bestMove = new MoveContent(alpha, move.startPosition, move.endPosition);
}
}
// return
the best score
return alpha;
} // AlphaBeta()
}
This is
the makeMove method
public void makeMove(int startPosition, int endPosition) {
// quick reference to selected piece and attacked piece
Piece selectedPiece = null;
if (!(chessBoard[startPosition].square.isEmpty())) {
selectedPiece = chessBoard[startPosition].square.firstElement();
}
Piece attackedPiece = null;
if (!(chessBoard[endPosition].square.isEmpty())) {
attackedPiece = chessBoard[endPosition].square.firstElement();
}
// if a piece is taken, amend score
if (!(chessBoard[endPosition].square.isEmpty()) && attackedPiece != null) {
if (attackedPiece.pieceColour == PieceColour.White) {
blackScore = blackScore + attackedPiece.pieceValue;
}
if (attackedPiece.pieceColour == PieceColour.Black) {
whiteScore = whiteScore + attackedPiece.pieceValue;
}
}
// actually move
the piece
chessBoard[endPosition].square.removeAllElements();
chessBoard[endPosition].addPieceToSquare(selectedPiece);
chessBoard[startPosition].square.removeAllElements();
// changing piece colour based on
position
if (endPosition > 15) {
selectedPiece.pieceColour = PieceColour.White;
}
if (endPosition <= 15) {
selectedPiece.pieceColour = PieceColour.Black;
}
//change to other player
if (whosMove == PieceColour.Black) whosMove = PieceColour.White;
else if (whosMove == PieceColour.White) whosMove = PieceColour.Black;
} // makeMove()
