private static Task <Move> FindBestMove(IEnumerable <Move> moves,
int[][] cells,
int color,
int depth)
{
return(Task.Run <Move>(() =>
{
Move bestMove = null;
int bestscore = int.MinValue;
if (moves != null)
{
foreach (var move in moves)
{
var copy = Reversi.Clone(cells);
Reversi.TryPlay(copy, move);
// find the best move our opponent can make. Hence, the minus sign.
int ss = -Score(copy, 0, -color, depth, false);
if (ss > bestscore)
{
bestscore = ss;
bestMove = move;
}
}
}
return bestMove;
}));
}
private static int Score(int[][] cells,
int d,
int color,
int depth,
bool pass // true means our opponent did not have any move to play; he passed
)
{
int other = -color;
if (d > depth)
{
// time to stop recursion
int s = 0;
for (int i = 0; i < _corners.Length; i++)
{
var corner = _corners[i];
var xsquare = _xsquares[i];
var q = cells[corner.Row][corner.Col];
if (q == color)
{
s += 300;
}
else if (q == other)
{
s -= 300;
}
else
{
q = cells[xsquare.Row][xsquare.Col];
if (q == color)
{
s -= 50;
}
else if (q == other)
{
s += 50;
}
}
}
return(s);
}
int bestScore = int.MinValue;
int n = 0; // will store the # of valid moves we can make
for (int row = 0; row < Board.ROWS; row++)
{
for (int col = 0; col < Board.COLS; col++)
{
var copy = Reversi.Clone(cells);
var move = new Move {
Row = row, Col = col, Color = color, PositionsToFlip = Reversi.GetPositionsToFlip(row, col, color, copy)
};
if (Reversi.TryPlay(copy, move))
{
n++;
// find the score our opponent can make.
int ss = -Score(copy, d + 1, other, depth, false);
if (ss > bestScore)
{
bestScore = ss;
}
}
}
}
if (n == 0)
{
// there is no valid move that we can play. we can't set bestPos to any meaningful value.
if (pass)
{
// opponent also had no move to play
// this means game will end
for (int i = 0; i < Board.ROWS; i++)
{
for (int j = 0; j < Board.COLS; j++)
{
if (cells[i][j] == color)
{
n++;
}
else if (cells[i][j] == other)
{
n--;
}
}
}
if (n > 0)
{
// we will win.
return(n + 8000);
}
else
{
// we will lose.
return(n - 8000);
}
}
else
{
bestScore = -Score(cells, d + 1, other, depth, true);
}
}
if (d >= depth - 1)
{
return(bestScore + (n << 3));
}
else
{
return(bestScore);
}
}