public Tuple <int, int> GetNextMove(int[,] game, int level, bool whiteTurn)
{
int[,] gameState = new int[9, 7];
for (int i = 0; i < 9; i++)
{
for (int j = 0; j < 7; j++)
{
gameState[i, j] = game[i, j];
}
}
AIBoard logic = new AIBoard
{
GameBoard = gameState,
PlayerTurn = whiteTurn ? Player.White : Player.Black
};
List <IntPosition> possibleMoves = logic.GetAllPossibleMoves();
if (possibleMoves.Count == 0)
{
return(new Tuple <int, int>(-1, -1));
}
var nextMove = AlphaBeta(logic, level, int.MaxValue, true);
return(new Tuple <int, int>(nextMove.Item2.Column, nextMove.Item2.Row));
}
/// <summary>
/// Simple alpha-beta algorithm
/// </summary>
/// <param name="nodeBoard">A particular game state</param>
/// <param name="depth">The maximum tree depth</param>
/// <param name="parentValue"></param>
/// <param name="maximizingPlayer"></param>
/// <returns></returns>
private Tuple <int, IntPosition> AlphaBeta(AIBoard nodeBoard, int depth, int parentValue, bool maximizingPlayer)
{
if (depth == 0 || nodeBoard.IsTerminal())
{
return(new Tuple <int, IntPosition>(nodeBoard.CurrentPlayerData.NumberOfPawns, new IntPosition(-1, -1)));
}
else
{
int optVal = maximizingPlayer ? -int.MaxValue : int.MaxValue;
IntPosition optOp = new IntPosition(-1, -1);
var childPositions = nodeBoard.GetAllPossibleMoves();
foreach (var child in childPositions)
{
var returnVal = AlphaBeta(PosToBoard(child, nodeBoard), depth - 1, optVal, !maximizingPlayer);
int minOrMax = maximizingPlayer ? 1 : -1;
if (returnVal.Item1 * minOrMax > optVal * minOrMax)
{
optVal = returnVal.Item1;
optOp = child;
if (optVal * minOrMax > parentValue * minOrMax)
{
break;
}
}
}
return(new Tuple <int, IntPosition>(optVal, optOp));
}
}
/// <summary>
/// Creates an AIBoard class given the position of a move to play
/// and the board where the move has to be played.
/// </summary>
/// <param name="position">The position of the pawn to play on the board</param>
/// <param name="sourceBoard">The board where the move takes place</param>
/// <returns>A new AIBoard with the updated game state</returns>
private AIBoard PosToBoard(IntPosition position, AIBoard sourceBoard)
{
AIBoard newBoard = new AIBoard
{
GameBoard = sourceBoard.GameBoard,
PlayerTurn = sourceBoard.PlayerTurn
};
newBoard.PlayMove(position.Column, position.Row, PlayerTurn == Player.White);
return(newBoard);
}
