public AlphaBetaReturnValue MinValue(CheckersBoard board, int alphaValue, int betaValue, PieceColor color, ref int currentDepth, ref int maxDepth, int maxDepthToSearchFor)
{
NodesGenerated++;
var v = new AlphaBetaReturnValue(PositiveInfinity, null, currentDepth + 1);
var moves = board.GetAllAvailableMoves(color).ToList().OrderByDescending(mr => mr.JumpResults.Count()).ToList();
var coTest = CutoffTest(board, currentDepth, maxDepthToSearchFor);
if (coTest.HasValue && coTest.Value || !moves.Any())
{
v.Value = Evaluate(board, color);
v.Depth = currentDepth;
return v;
}
if (!coTest.HasValue)
{
return null;
}
for (var i = 0; i < moves.Count; i++)
{
var m = moves[i];
board.MovePiece(m, color);
if (currentDepth == 0 && moves.Count == 1)
{
v.Move = m;
v.Value = Evaluate(board, color);
board.RevertMove(m, color);
return v;
}
var newDepth = currentDepth;
newDepth++;
var retVal = MaxValue(board, alphaValue, betaValue,
color == PieceColor.Black ? PieceColor.Red : PieceColor.Black, ref newDepth,
ref maxDepth, maxDepthToSearchFor);
if (retVal == null)
return null;
retVal.Move = m;
board.RevertMove(m, color);
if (retVal.Depth > maxDepth)
maxDepth = retVal.Depth;
if(retVal.Value < v.Value)
{
v.Value = retVal.Value;
v.Move = retVal.Move;
}
if (v.Value <= alphaValue)
{
NumberOfMinPrunes++;
return retVal;
}
betaValue = Math.Min(betaValue, v.Value);
}
return v;
}
// the evaluation function sums up the values of the pieces for each color and the available moves
// the available moves is weighted more, and the value of the piece is determined by how close the piece is to the center of the board [favors pieces that are in the center]
public int Evaluate(CheckersBoard state, PieceColor color)
{
int pOne = 0, pTwo = 0;
for (var i = 0; i < state.Pieces.AlivePlayerOnePieces.Count; i++)
{
var piece = state.Pieces.AlivePlayerOnePieces[i];
pOne += 3*(state.TileBoard.Height >> 1 - Math.Abs(state.TileBoard.Height >> 1 - piece.Y)) +
3*(state.TileBoard.Width >> 1 - Math.Abs(state.TileBoard.Width >> 1 - piece.X));
}
for (var i = 0; i < state.Pieces.AlivePlayerTwoPieces.Count; i++)
{
var piece = state.Pieces.AlivePlayerTwoPieces[i];
pTwo += 3*(state.TileBoard.Height >> 1 - Math.Abs(state.TileBoard.Height >> 1 - piece.Y)) +
3*(state.TileBoard.Width >> 1 - Math.Abs(state.TileBoard.Width >> 1 - piece.X));
}
pOne += state.GetAllAvailableMoves(PieceColor.Black).Count()*10;
pTwo += state.GetAllAvailableMoves(PieceColor.Red).Count()*10;
return (Color == PieceColor.Black ? pOne - pTwo : pTwo - pOne);
}