public List <MoveSequence> AlphaBetaRecursive(Board board, int depth, bool isWhite)
{
var sw = System.Diagnostics.Stopwatch.StartNew();
var result = new List <MoveSequence>();
_numberOfLeafEvaluations = 0;
_numberOfBranchesPruned = 0;
MoveSequence alpha = new MoveSequence {
Value = float.NegativeInfinity
};
MoveSequence beta = new MoveSequence {
Value = float.PositiveInfinity
};
board.RecalculateScore();
var moves = board.GetMovesForPlayer(isWhite ? EnumBoardSquare.White : EnumBoardSquare.Black);
if (isWhite)
{
moves = moves.OrderByDescending(x => x.ScoreChange).ToArray();
}
else
{
moves = moves.OrderBy(x => x.ScoreChange).ToArray();
}
foreach (var move in moves)
{
var scoreChange = AlphaBetaRecursive(board, move, depth - 1, alpha, beta, !isWhite);
result.Add(scoreChange);
}
//Parallel.ForEach(moves, (Move move) =>
//{
// var scoreChange = AlphaBetaRecursive(board, move, depth - 1, alpha, beta, !isWhite);
// lock (_lock)
// {
// result.Add(scoreChange);
// }
//});
_durationMilliseconds = sw.ElapsedMilliseconds;
if (isWhite)
{
return(Shuffle(result).OrderByDescending(x => x.Value).ToList());
}
else
{
return(Shuffle(result).OrderBy(x => x.Value).ToList());
}
}
private MoveSequence AlphaBetaRecursive(Board previousBoard, Move move, int depth, MoveSequence alpha, MoveSequence beta, bool isWhite)
{
if (depth == 0 || (move.PieceCaptured & EnumBoardSquare.King) == EnumBoardSquare.King)
{
_numberOfLeafEvaluations++;
return(new MoveSequence
{
Value = previousBoard.Score + move.ScoreChange,
Move = move,
NextMove = null
});
}
if (isWhite)
{
Board board = previousBoard.MakeMove(move);
var moves = board.GetMovesForPlayer(EnumBoardSquare.White);
Array.Sort(moves, (x, y) => y.ScoreChange.CompareTo(x.ScoreChange));
for (int i = 0; i < moves.Length; i++)
{
if (_boardStates.TryGetValue(board.GetHashCode(), out var info) && info.SearchDepth == depth)
{
if (alpha.Value < info.Value)
{
if (info.Value >= beta.Value)
{
_numberOfBranchesPruned++;
return(beta);
}
else
{
alpha = new MoveSequence {
Move = move, Value = info.Value, NextMove = null
};
}
}
}
else
{
var moveSequence = AlphaBetaRecursive(board, moves[i], depth - 1, alpha, beta, false);
if (alpha.Value < moveSequence.Value)
{
if (moveSequence.Value >= beta.Value)
{
_numberOfBranchesPruned++;
return(beta);
}
else
{
alpha = new MoveSequence {
Move = move, Value = moveSequence.Value, NextMove = moveSequence
};
}
}
lock (_lock)
{
if (!_boardStates.ContainsKey(board.GetHashCode()))
{
_boardStates.Add(board.GetHashCode(), new BoardStateInfo {
SearchDepth = depth, Value = moveSequence.Value
});
}
}
}
}
return(alpha);
}
else
{
Board board = previousBoard.MakeMove(move);
var moves = board.GetMovesForPlayer(EnumBoardSquare.Black);
Array.Sort(moves, (x, y) => x.ScoreChange.CompareTo(y.ScoreChange));
for (int i = 0; i < moves.Length; i++)
{
if (_boardStates.TryGetValue(board.GetHashCode(), out var info) && info.SearchDepth == depth)
{
if (info.Value < beta.Value)
{
if (alpha.Value >= info.Value)
{
_numberOfBranchesPruned++;
return(alpha);
}
else
{
beta = new MoveSequence {
Move = move, Value = info.Value, NextMove = null
};
}
}
}
else
{
var moveSequence = AlphaBetaRecursive(board, moves[i], depth - 1, alpha, beta, true);
if (moveSequence.Value < beta.Value)
{
if (alpha.Value >= moveSequence.Value)
{
_numberOfBranchesPruned++;
return(alpha);
}
else
{
beta = new MoveSequence {
Move = move, Value = moveSequence.Value, NextMove = moveSequence
};
}
}
lock (_lock)
{
if (!_boardStates.ContainsKey(board.GetHashCode()))
{
_boardStates.Add(board.GetHashCode(), new BoardStateInfo {
SearchDepth = moveSequence.Length, Value = moveSequence.Value
});
}
}
}
}
return(beta);
}
}
