protected static bool ImmediateBlock(Piece inPiece, TicTacToeBoard inBoard, ref ushort bestMove)
{
Piece p = (inPiece.Value == Piece.PieceValue.X) ? new Piece(Piece.PieceValue.X) : new Piece(Piece.PieceValue.O);
for (ushort i = 0; i < inBoard.Length; ++i)
{
// create a clone of the current board
TicTacToeBoard tempBoard = new TicTacToeBoard(inBoard);
tempBoard.Place(p, i);
if (tempBoard.Win(p.Value))
{
bestMove = i;
return(true);
}
}
return(false);
}
protected static bool ImmediateWin(Piece inPiece, TicTacToeBoard inBoard, ref ushort bestMove)
{
for (ushort i = 0; i < inBoard.Length; ++i)
{
// create a clone of the current board
TicTacToeBoard tempBoard = new TicTacToeBoard(inBoard);
// place a piece on each sqaure in the new board
tempBoard.Place(inPiece, i);
// and see if it results in an immediate win
if (tempBoard.Win(inPiece.Value))
{
bestMove = i;
return(true);
}
}
return(false);
}
protected static MoveStrategy LookAhead(Piece inPiece, TicTacToeBoard inBoard, ref ushort bestMove)
{
// unused dummy value to seend the algorithm
ushort aDummy = 0;
// temporary strategy
MoveStrategy aResponse;
// the strategy to return
MoveStrategy outValue = (inPiece.Value == Piece.PieceValue.X) ? MoveStrategy.OWin - 1 : MoveStrategy.XWin + 1;
// first check to see if the game is a draw
if (inBoard.Full())
{
outValue = MoveStrategy.Draw;
}
// return any move that results in an immediate win
else if (Computer.ImmediateWin(inPiece, inBoard, ref bestMove))
{
outValue = (inPiece.Value == Piece.PieceValue.X) ? MoveStrategy.XWin : MoveStrategy.OWin;
}
// return any move that will result in blocking the other player from an immediate win on his next turn
else if (Computer.ImmediateBlock(inPiece, inBoard, ref bestMove))
{
outValue = (inPiece.Value == Piece.PieceValue.X) ? MoveStrategy.XBlock : MoveStrategy.OBlock;
}
// no immediate wins so look for a promising move
else
{
for (ushort i = 0; i < inBoard.Length; ++i)
{
if (!inBoard.At(i))
{
inBoard.Place(inPiece, i);
// swap pieces and go down a move
Piece aPiece = (inPiece.Value == Piece.PieceValue.X) ? new Piece(Piece.PieceValue.O) : new Piece(Piece.PieceValue.X);
// call look ahead recursively with a copy of the board each time
aResponse = LookAhead(aPiece, new TicTacToeBoard(inBoard), ref aDummy);
// determine the best move
switch (inPiece.Value)
{
case Piece.PieceValue.X:
if (aResponse > outValue)
{
outValue = aResponse;
bestMove = i;
}
break;
case Piece.PieceValue.O:
if (aResponse < outValue)
{
outValue = aResponse;
bestMove = i;
}
break;
default:
break;
} // end switch
} // end if
} // end for loop
} // end else
// return the best move strategy
return(outValue);
}
