private int NoParitySearch(BitBoard board, int alpha, int beta, int empties, bool prevmove = true)
{
searchResult.Nodes++;
var moves = Rule.FindMoves(board);
if (moves.Length == 0)
{
if (!prevmove)
{
//END
return(EndGameEvaluation.Eval(board));
}
else
{
return(-NoParitySearch(board.Switch(), -beta, -alpha, empties, false));
}
}
var score = minimumScore;
var diffCount = board.DiffCount();
foreach (var pos in moves)
{
var eval = 0;
var flips = Rule.FindFlips(board, pos);
var oppBoard = Rule.FlipSwitch(board, pos, flips);
var ownFlipsCount = flips.CountBits();
if (empties == 2)
{
//the last move of opponent player
var lastEmptySquare = oppBoard.EmptyPieces.Index();
if (lastEmptySquare < 0)
{
throw new Exception($"invalid square index:{lastEmptySquare}");
}
var oppFlipsCount = Rule.CountFlips(oppBoard, lastEmptySquare);
if (oppFlipsCount > 0)
{
//both done.
eval = diffCount + 2 * (ownFlipsCount - oppFlipsCount);
}
else
{
//opp pass
var ownLastFlipsCount = Rule.CountFlips(oppBoard, lastEmptySquare);
if (ownLastFlipsCount > 0)
{
eval = diffCount + 2 * (ownFlipsCount + ownLastFlipsCount) + 2;
}
else
{
//all pass
eval = diffCount + 2 * ownFlipsCount;
//TODO: eval==0?
if (eval >= 0)
{
eval += 2;
}
}
}
}
else
{
//empties!=2
eval = -NoParitySearch(oppBoard, -beta, -alpha, empties - 1);
}
if (eval > score)
{
score = eval;
if (eval > alpha)
{
if (eval >= beta)
{
return(score);
}
alpha = eval;
}
}
}
return(score);
}
public int Eval(BitBoard board)
{
return(board.DiffCount());
}