private float Alphabeta(Board board, Disc playerToMove, int distanceToLeafNodes, float alpha, float beta)
{
if (distanceToLeafNodes == 0)
{
NodesEvaluated++;
return _nodeEvaluator.Evaluate(playerToMove, board);
}
float best = float.MinValue;
foreach (Square move in board.Moves(playerToMove))
{
if (best >= beta)
{
BetaCutoffs++;
break;
}
var childBoard = new Board(board);
childBoard.MakeMove(playerToMove, move);
if (best > alpha) alpha = best;
float score = -Alphabeta(childBoard, playerToMove.Opponent(), distanceToLeafNodes - 1, -beta, -alpha);
if (score > best)
{
best = score;
if (distanceToLeafNodes == _currentSearchDepth)
{
BestScore = score;
BestMove = move;
}
}
}
return best;
}
public Board(Board board)
{
//Copy members
for (int row = 0; row < 8; row++)
for (int col = 0; col < 8; col++)
_squares[row, col] = board._squares[row, col];
_squaresRemaining = CountDiscs(Disc.None);
}
public override float Evaluate(Disc playerToMove, Board board)
{
int divisor = 0;
float total = 0;
foreach (var evaluator in Evaluators)
{
total += evaluator.Evaluate(playerToMove, board);
divisor += evaluator.Weight;
}
if (divisor == 0) return 0;
return total / divisor;
}
public override float Evaluate(Disc playerToMove, Board board)
{
NodesEvaluated = 0;
BetaCutoffs = 0;
if (IterativeDeepening) _currentSearchDepth = 1;
else _currentSearchDepth = MaxSearchDepth;
while (_currentSearchDepth <= MaxSearchDepth)
{
_currentSearchDepth++;
Alphabeta(board, playerToMove, _currentSearchDepth, float.MinValue, float.MaxValue);
}
return BestScore;
}
public override float Evaluate(Disc playerToMove, Board board)
{
int movesAvailable = board.Moves(playerToMove).Length;
return (float) Math.Min(Math.Pow(movesAvailable - 4, 3), 20);
}
public abstract string GetMove(Board game);
public override string GetMove(Board game)
{
return "a1";
}
public override float Evaluate(Disc playerToMove, Board board)
{
return Evaluator.Evaluate(playerToMove, board) * Weight;
}
public abstract float Evaluate(Disc playerToMove, Board board);
