/// <summary>
/// Over all rows sums the number of pieces in the row if
/// the specified piece can still win in that row i.e. the row
/// does not contain an opponent's piece.
/// </summary>
/// <param name="board">The board.</param>
/// <param name="piece">The piece.</param>
/// <returns>A value that evaluates the columns.</returns>
private static double EvaluateColumns(Board board, Pieces piece)
{
var score = 0.0;
// Check the rows
for (var j = 0; j < Board.Columns; j++)
{
var count = 0;
var rowClean = true;
for (var i = 0; i < Board.Columns; i++)
{
var boardPiece = board.GetPieceAtPoint(i, j);
if (boardPiece == piece)
{
count++;
}
else if (boardPiece == OpponentPieceHelper.GetOpponentPiece(piece))
{
rowClean = false;
break;
}
}
// If we get here then the row is clean (an open row)
if (rowClean && count != 0)
{
// Math.Pow(count, count);
score += count;
}
}
return(score);
}
/// <inheritdoc cref="Node"/>
/// <summary>
/// Evaluates the value of the node using the evaluation function.
/// </summary>
/// <seealso cref="Node"/>
protected override void Evaluate()
{
if (this.Board is null)
{
throw new ArgumentNullException(nameof(this.Board), "The board wasn't initialized properly.");
}
this.Value = this.EvaluatorLocal?.Evaluate(this.Board, OpponentPieceHelper.GetOpponentPiece(this.MyPieceLocal)) ?? -1;
}
/// <summary>
/// Evaluates the favorability of the current board configuration for maxPiece. Higher values
/// indicate better configuration for maxPiece.
/// </summary>
/// <param name="b">The game board to evaluate.</param>
/// <param name="maxPiece">The piece representing the maximum.</param>
/// <returns>A <see cref="double"/> that evaluates the result.</returns>
public double Evaluate(Board b, Pieces maxPiece)
{
this.FunctionCalls++;
if (b.HasWinner())
{
return(b.WinningPiece == maxPiece ? double.MaxValue : double.MinValue);
}
var maxValue = EvaluatePiece(b, maxPiece);
var minValue = EvaluatePiece(b, OpponentPieceHelper.GetOpponentPiece(maxPiece));
return(maxValue - minValue);
}
/// <summary>
/// Over both diagonals sums the number of pieces in the diagonal if
/// the specified piece can still win in that diagonal i.e. the diagonal
/// does not contain an opponent's piece.
/// </summary>
/// <param name="board">The board.</param>
/// <param name="piece">The piece.</param>
/// <returns>A value that evaluates the diagonals.</returns>
private static double EvaluateDiagonals(Board board, Pieces piece)
{
// Go down and to the right diagonal first
var count = 0;
var diagonalClean = true;
var score = 0.0;
for (var i = 0; i < Board.Columns; i++)
{
var boardPiece = board.GetPieceAtPoint(i, i);
if (boardPiece == piece)
{
count++;
}
if (boardPiece != OpponentPieceHelper.GetOpponentPiece(piece))
{
continue;
}
diagonalClean = false;
break;
}
if (diagonalClean && count > 0)
{
// Math.Pow(count, count);
score += count;
}
// Now try the other way
var row = 0;
var col = 2;
count = 0;
diagonalClean = true;
while (row < Board.Rows && col >= 0)
{
var boardPiece = board.GetPieceAtPoint(row, col);
if (boardPiece == piece)
{
count++;
}
if (boardPiece == OpponentPieceHelper.GetOpponentPiece(piece))
{
diagonalClean = false;
break;
}
row++;
col--;
}
if (count > 0 && diagonalClean)
{
score += count;
}
return(score);
}