Day09.java

void main() {
    var input = readInput();
    
    var rectangles = IntStream.range(0, input.size() - 1).boxed().flatMap(i -> IntStream.range(i + 1, input.size()).mapToObj(j -> Rectangle.fromCoords(input.get(i), input.get(j)))).toList();
    IO.println(rectangles.stream().mapToLong(Rectangle::area).max().orElseThrow());
    
    var lines = IntStream.range(0, input.size()).mapToObj(i -> Rectangle.fromCoords(input.get(i), input.get((i + 1) % input.size()))).toList();
    IO.println(rectangles.stream().filter(r -> lines.stream().noneMatch(r::isOverlap)).mapToLong(Rectangle::area).max().orElseThrow());
}

record Coord(long x, long y) {
    static Coord fromStr(String str) {
        var parts = str.split(",");
        return new Coord(Long.parseLong(parts[0]), Long.parseLong(parts[1]));
    }
}

record Rectangle(Coord min, Coord max) {
    boolean isOverlap(Rectangle other) {
        return min.x < other.max.x && max.x > other.min.x && min.y < other.max.y && max.y > other.min.y;
    }
    long area() {
        return (max.x - min.x + 1) * (max.y - min.y + 1);
    }
    static Rectangle fromCoords(Coord a, Coord b) {
        return new Rectangle(new Coord(Math.min(a.x, b.x), Math.min(a.y, b.y)), new Coord(Math.max(a.x, b.x), Math.max(a.y, b.y)));
    }
}

List<Coord> readInput() {
    try (var stream = Files.lines(Path.of("input_09.txt"), StandardCharsets.UTF_8)) {
        return stream.map(Coord::fromStr).toList();
    } catch (IOException e) {
        throw new RuntimeException(e);
    }
}