public static int Heuristic(ulong board, bool max_for_white, List <ulong> possible_moves = null)
{
if (!Board.IsPlacementPhase(board))
{
if (Board.IsWhiteTurn(board) && Board.WhitePiecesOnBoard(board) < 3)
{
if (max_for_white)
{
return(-1000);
}
else
{
return(1000);
}
}
else if (!Board.IsWhiteTurn(board) && Board.BlackPiecesOnBoard(board) < 3)
{
if (max_for_white)
{
return(1000);
}
else
{
return(-1000);
}
}
}
if (possible_moves == null)
{
possible_moves = Board.GetMoves(board);
}
if (possible_moves.Count == 0)
{
if (Board.IsWhiteTurn(board))
{
if (max_for_white)
{
return(-1000);
}
else
{
return(1000);
}
}
else
{
if (max_for_white)
{
return(1000);
}
else
{
return(-1000);
}
}
}
/* We score +1 for a move, +2 if it forms a mill */
int score = 0;
var old_runs = Board.GetRunPieces(board);
foreach (var move in possible_moves)
{
var new_runs = Board.GetRunPieces(move);
if (new_runs != old_runs && Board.CountBits(new_runs) >= Board.CountBits(old_runs))
{
score += 5;
}
else
{
score++;
}
}
if (Board.IsWhiteTurn(board))
{
if (max_for_white)
{
return(score);
}
else
{
return(-score);
}
}
else
{
if (max_for_white)
{
return(-score);
}
else
{
return(score);
}
}
}
int alphabeta(ulong board, int depth, int alpha, int beta, bool maximizingPlayer, out ulong move)
{
if (cache_v[depth].TryGetValue(board, out var cached))
{
move = cache_move[depth][board]; return(cached);
}
var children = Board.GetMoves(board);
if (depth == 0 || Board.CurrentPlayerHasLessThanThree(board) || children.Count == 0)
{
move = 0UL;
return(Heuristic(board, IsWhite, children));
}
if (maximizingPlayer)
{
var bestValue = int.MinValue;
ulong best_move = 0UL;
foreach (var child in children)
{
var v = alphabeta(child, depth - 1, alpha, beta, false, out var unused);
if (v > bestValue)
{
if (v > alpha)
{
alpha = v;
}
bestValue = v;
best_move = child;
}
if (beta <= alpha)
{
break;
}
}
move = best_move;
cache_v[depth][board] = bestValue;
cache_move[depth][board] = move;
return(bestValue);
}
else
{
// minimizing player
var bestValue = int.MaxValue;
ulong best_move = 0UL;
foreach (var child in children)
{
var v = alphabeta(child, depth - 1, alpha, beta, true, out var unused);
if (v < bestValue)
{
if (v < beta)
{
beta = v;
}
bestValue = v;
best_move = child;
}
if (beta <= alpha)
{
break;
}
}
move = best_move;
cache_v[depth][board] = bestValue;
cache_move[depth][board] = move;
return(bestValue);
}
}