public List <Board> GenerateSafeBoards(bool includeCheckmates)
{
List <Board> boards = this.GenerateSubBoards();
Board workingBoard = new Board();
for (int k = 0; k < boards.Count; k++)
{
workingBoard.Copy(boards[k]);
foreach (Board b in workingBoard.GenerateSubBoards())
{
if (b.GetWinner() == workingBoard.CurrentPlayer)
{
boards.RemoveAt(k);
k--;
break;
}
if (includeCheckmates &&
BoardEvaluator.HasCheckmate(b, workingBoard.CurrentPlayer))
{
boards.RemoveAt(k);
k--;
break;
}
}
}
return(boards);
}
// Negamax style alpha beta pruning search
private int AlphaBeta(Board b, int depth, int alpha, int beta)
{
if (depth == 0)
{
return(-b.Evaluation);
}
switch (b.GetWinner())
{
case PieceColor.White:
return((b.CurrentPlayer == PieceColor.White) ? BoardEvaluator.EVAL_WHITE_WIN : -BoardEvaluator.EVAL_WHITE_WIN);
case PieceColor.Black:
return((b.CurrentPlayer == PieceColor.White) ? BoardEvaluator.EVAL_BLACK_WIN : -BoardEvaluator.EVAL_BLACK_WIN);
case PieceColor.Both:
return(BoardEvaluator.EVAL_DRAW);
case PieceColor.Empty:
break;
}
List <Board> boards = b.GenerateSubBoards();
if (boards.Count == 0)
{
return(NOMOVES);
}
positionsEvaluated += boards.Count;
BoardEvaluator.SortBoards(ref boards);
int current;
int best = MINSCORE;
int localAlpha = alpha;
for (int i = 0; i < boards.Count; i++)
{
current = -AlphaBeta(boards[i], depth - 1, -beta, -localAlpha);
if (current == -NOMOVES)
{
current = boards[i].Evaluation;
}
best = Math.Max(current, best);
if (best >= beta)
{
return(beta);
}
if (best > localAlpha)
{
localAlpha = best;
}
}
return(best);
}
// Finds all unique boards possible after applying a move by the current player
public List <Board> GenerateSubBoards()
{
Dictionary <Board, int> boards = new Dictionary <Board, int>(256);
if (this.GetWinner() != PieceColor.Empty)
{
return(new List <Board>());
}
Board b = new Board(this);
for (int i = 0; i < 6; i++)
{
for (int j = 0; j < 6; j++)
{
if (this.GetColorAt(i, j) == PieceColor.Empty)
{
b.Copy(this);
b.ApplyMoveFast(i, j, this.CurrentPlayer, Rotation.LowerLeftAntiClockwise);
if (!boards.ContainsKey(b))
{
b.Evaluation = BoardEvaluator.Evaluate(ref b);
boards.Add(new Board(b), 0);
}
b.Copy(this);
b.ApplyMoveFast(i, j, this.CurrentPlayer, Rotation.LowerLeftClockwise);
if (!boards.ContainsKey(b))
{
b.Evaluation = BoardEvaluator.Evaluate(ref b);
boards.Add(new Board(b), 0);
}
b.Copy(this);
b.ApplyMoveFast(i, j, this.CurrentPlayer, Rotation.LowerRightAntiClockwise);
if (!boards.ContainsKey(b))
{
b.Evaluation = BoardEvaluator.Evaluate(ref b);
boards.Add(new Board(b), 0);
}
b.Copy(this);
b.ApplyMoveFast(i, j, this.CurrentPlayer, Rotation.LowerRightClockwise);
if (!boards.ContainsKey(b))
{
b.Evaluation = BoardEvaluator.Evaluate(ref b);
boards.Add(new Board(b), 0);
}
b.Copy(this);
b.ApplyMoveFast(i, j, this.CurrentPlayer, Rotation.UpperLeftAntiClockwise);
if (!boards.ContainsKey(b))
{
b.Evaluation = BoardEvaluator.Evaluate(ref b);
boards.Add(new Board(b), 0);
}
b.Copy(this);
b.ApplyMoveFast(i, j, this.CurrentPlayer, Rotation.UpperLeftClockwise);
if (!boards.ContainsKey(b))
{
b.Evaluation = BoardEvaluator.Evaluate(ref b);
boards.Add(new Board(b), 0);
}
b.Copy(this);
b.ApplyMoveFast(i, j, this.CurrentPlayer, Rotation.UpperRightAntiClockwise);
if (!boards.ContainsKey(b))
{
b.Evaluation = BoardEvaluator.Evaluate(ref b);
boards.Add(new Board(b), 0);
}
b.Copy(this);
b.ApplyMoveFast(i, j, this.CurrentPlayer, Rotation.UpperRightClockwise);
if (!boards.ContainsKey(b))
{
b.Evaluation = BoardEvaluator.Evaluate(ref b);
boards.Add(new Board(b), 0);
}
}
}
}
return(new List <Board>(boards.Keys));
}
public override Board Play(Board b)
{
if (b.CurrentPlayer != this.Color)
{
throw new InvalidOperationException();
}
Debug.Assert(false, b.ToString());
List <Board> boards;
if (maxDepth == 2)
{
boards = b.GenerateSafeBoards(true);
}
else
{
boards = b.GenerateSafeBoards();
}
Debug.WriteLine("Safe moves: " + boards.Count.ToString());
// if opponent wins on their next move no matter what
if (boards.Count == 0)
{
// if we have a legal move, do it even though it's a loser
boards = b.GenerateSubBoards();
if (boards.Count == 0)
{
return(b);
}
return(boards[0]);
}
BoardEvaluator.SortBoards(ref boards);
int current;
int localAlpha = MINSCORE;
Board bestBoard = boards[0];
DateTime startTime = DateTime.Now;
positionsEvaluated = 0;
for (int i = 0; i < boards.Count; i++)
{
// Console.Write("+");
current = -AlphaBeta(boards[i], maxDepth, MINSCORE, -localAlpha);
if (current == -NOMOVES)
{
current = boards[i].Evaluation;
}
if (current > localAlpha)
{
localAlpha = current;
bestBoard = boards[i];
if (current == BoardEvaluator.EVAL_WHITE_WIN)
{
break;
}
}
}
DateTime endTime = DateTime.Now;
TimeSpan moveTime = endTime - startTime;
//Console.WriteLine(" Score: " + localAlpha.ToString());
//Console.WriteLine("Time: {0}", moveTime.TotalSeconds);
//Console.WriteLine("Moves evaluated: {0}", positionsEvaluated);
//Console.WriteLine("Moves/sec: {0}", positionsEvaluated / moveTime.TotalSeconds);
Debug.Assert(false, bestBoard.ToString());
return(bestBoard);
}
public override Board Play(Board b)
{
if (b.CurrentPlayer != this.Color)
{
throw new InvalidOperationException();
}
List <Board> boards = b.GenerateSafeBoards(true);
Debug.WriteLine("Safe moves: " + boards.Count.ToString());
// if opponent wins on their next move no matter what
if (boards.Count == 0)
{
// if we have a legal move, do it even though it's a loser
boards = b.GenerateSubBoards();
if (boards.Count == 0)
{
return(b);
}
return(boards[0]);
}
BoardEvaluator.SortBoards(ref boards);
int current;
int localAlpha = MINSCORE;
Board bestBoard = boards[0];
Board bestBoardLastCompletedDepth = boards[0];
int lastCompletedDepth = 1;
int lastCompletedDepthScore = 0;
startTime = DateTime.Now;
for (int depth = 1; depth < 36; depth++)
{
localAlpha = MINSCORE;
int i;
for (i = 0; i < boards.Count; i++)
{
current = -AlphaBeta(boards[i], depth, MINSCORE, -localAlpha);
if (current == -TIMEUP)
{
break;
}
if (current == -NOMOVES)
{
current = boards[i].Evaluation;
}
boards[i].Evaluation = current;
if (current > localAlpha)
{
localAlpha = current;
bestBoard = boards[i];
if (current == BoardEvaluator.EVAL_WHITE_WIN)
{
lastCompletedDepth = depth;
lastCompletedDepthScore = current;
bestBoardLastCompletedDepth = bestBoard;
break;
}
}
}
// bail from the loop if we didn't make it
// all the way through the search at this depth
if (i != boards.Count)
{
break;
}
// otherwise save the best move
lastCompletedDepthScore = localAlpha;
lastCompletedDepth = depth;
bestBoardLastCompletedDepth = bestBoard;
// re-sort the boards after each completed depth
// to increase the number of cutoffs at the next depth
BoardEvaluator.SortBoards(ref boards);
}
Debug.WriteLine(String.Format("Depth: {0} Score: {1}", lastCompletedDepth, lastCompletedDepthScore));
return(bestBoardLastCompletedDepth);
}
