OpenChess

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public class KX_K implements Evaluator {

	// Drive defending king towards the edge of the board

	// @formatter:off
	private static final int MateTable[] = { 
		100, 90, 80, 70, 70, 80, 90, 100,
		 90, 70, 60, 50, 50, 60, 70,  90, 
		 80, 60, 40, 30, 30, 40, 60,  80, 
		 70, 50, 30, 20, 20, 30, 50,  70, 
		 70, 50, 30, 20, 20, 30, 50,  70, 
		 80, 60, 40, 30, 30, 40, 60,  80, 
		 90, 70, 60, 50, 50, 60, 70,  90, 
		100, 90, 80, 70, 70, 80, 90, 100
	};
	// @formatter:on

	// The attacking side is given a descending bonus based on distance between
	// the two kings in basic endgames.
	private static final int DistanceBonus[] = { 0, 0, 100, 80, 60, 40, 20, 10 };


	public boolean matches(ChessBoard pos) {
		ChessPieceCount pc = pos.pieceCount();
		if (pc.totalPieceValue() < 5 || (pc.totalPieceValue(WHITE) != 0 && pc.totalPieceValue(BLACK) != 0))
			return false;

		if (pc.totalPieceValue() == 6) {
			String pattern = pc.toString();
			if (pattern.equals("k2n-k") || pattern.equals("k-k2n"))
				return false;
		}
		return true;
	}

	public int evaluate(ChessBoard pos) {

		ChessPieceCount pc = pos.pieceCount();
		ChessColor stronger = pc.stronger();
		ChessColor weaker = stronger.opponent();

		assert (Material.computeMaterialNoPawns(pos, weaker) == 0);
		assert (pc.count(PAWN, weaker) == 0);
	
		// Stalemate detection with lone king
		if ((pos.whosTurn() == weaker) && !pos.isInCheck() && (0 == pos.getMoves().size())) {
			return VALUE_DRAW;
		}
	
		ChessSquare winnerKSq = pos.kingSquare(stronger);
		ChessSquare loserKSq = pos.kingSquare(weaker);
	
		int result = Material.computeMaterialNoPawns(pos, stronger) + pc.count(PAWN, stronger)
				* PawnValueEg + MateTable[loserKSq.ordinal()] + DistanceBonus[winnerKSq.distance(loserKSq)];
	
		if ((pc.count(QUEEN, stronger) > 0) || (pc.count(ROOK, stronger) > 0) || pos.hasBishopPair(stronger)) {
			result += VALUE_KNOWN_WIN;
		}
	
		return stronger == pos.whosTurn() ? result : -result;
	}
}