private TreeNode MiniMax(Board board, Double depth, Double alpha, Double beta, Boolean maximizer)
{
if(depth == 0)
{
return GetLeafNode(board, maximizer);
}
var pieces = board.GetPiecesForPlayer(board.PlayerTurn);
var bestScore = maximizer ? _minScore : _maxScore;
var bestMove = default(Move);
var moves = pieces.SelectMany(x => x.GetPossibleMoves(board));
if (!moves.Any())
{
if (board.PlayerHasCheck(board.PlayerTurn))
{
return new TreeNode(null, maximizer ? _maxScore : _minScore);
}
}
foreach (var mv in moves)
{
var newBoard = board.Copy();
newBoard.MakeMove(mv);
var newNode = MiniMax(newBoard, depth - 1, alpha, beta, !maximizer);
if (maximizer)
{
if(newNode.Score > bestScore)
{
bestScore = newNode.Score;
bestMove = mv;
}
alpha = Math.Max(alpha, bestScore);
if(beta <= alpha)
{
return new TreeNode(bestMove, bestScore);
}
}
else
{
if(newNode.Score < bestScore)
{
bestScore = newNode.Score;
bestMove = mv;
}
beta = Math.Min(beta, bestScore);
if(beta <= alpha)
{
return new TreeNode(bestMove, bestScore);
}
}
}
return new TreeNode(bestMove, bestScore);
}
public void GetNextMoveMustNotAlterBoard()
{
_board = new Board();
_board.Initialize();
for(int i = 0; i < 10; i++)
{
var origBoard = _board.Copy();
var mv = _miniMaxService.GetNextMove(_board);
Assert.IsTrue(_board.Equals(origBoard));
_board.MakeMove(mv);
}
}
public Move GetNextMove(Board board)
{
var newBoard = board.Copy();
return MiniMax(board, _maxDepth, _minScore, _maxScore, true).Move;
}