add hungry ai

app/src/main/java/chess/ai/PieceCost.java

@@ -0,0 +1,60 @@
+package chess.ai;
+
+import chess.model.Color;
+import chess.model.Piece;
+import chess.model.PieceVisitor;
+import chess.model.pieces.Bishop;
+import chess.model.pieces.King;
+import chess.model.pieces.Knight;
+import chess.model.pieces.Pawn;
+import chess.model.pieces.Queen;
+import chess.model.pieces.Rook;
+
+public class PieceCost implements PieceVisitor<Integer> {
+
+	private final Color player;
+
+	public PieceCost(Color color) {
+		this.player = color;
+	}
+
+	public int getCost(Piece piece) {
+		if (piece == null)
+			return 0;
+		int cost = visit(piece);
+		if (piece.getColor() == player)
+			cost = -cost;
+		return cost;
+	}
+
+	@Override
+	public Integer visitPiece(Bishop bishop) {
+		return 3;
+	}
+
+	@Override
+	public Integer visitPiece(King king) {
+		return 90;
+	}
+
+	@Override
+	public Integer visitPiece(Knight knight) {
+		return 3;
+	}
+
+	@Override
+	public Integer visitPiece(Pawn pawn) {
+		return 1;
+	}
+
+	@Override
+	public Integer visitPiece(Queen queen) {
+		return 9;
+	}
+
+	@Override
+	public Integer visitPiece(Rook rook) {
+		return 5;
+	}
+
+}