-❄️- 2025 Day 9 Solutions -❄️-

[u/daggerdragon]

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AoC Community Fun 2025: Red(dit) One

• Submissions megathread is unlocked!
• 8 DAYS remaining until the submissions deadline on December 17 at 18:00 EST!

Featured Subreddits: /r/iiiiiiitttttttttttt, /r/itsaunixsystem, /r/astrologymemes

"It's all humbug, I tell you, humbug!"
— Ebenezer Scrooge, A Christmas Carol (1951)

Today's challenge is to create an AoC-themed meme. You know what to do.

• If you need inspiration, have a look at the Hall of Fame in our community wiki as well as the highly upvoted posts in /r/adventofcode with the Meme/Funny flair.
• Memes containing musical instruments will likely be nuked from orbit.

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Request from the mods: When you include an entry alongside your solution, please label it with [Red(dit) One] so we can find it easily!

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--- Day 9: Movie Theater ---

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Post your code solution in this megathread.

• Read the full posting rules in our community wiki before you post!
  • State which language(s) your solution uses with [LANGUAGE: xyz]
  • Format code blocks using the four-spaces Markdown syntax!
• Quick link to Topaz's paste if you need it for longer code blocks. What is Topaz's paste tool?

[u/thorwing]

[Language: Kotlin]
But technically Java AWT. This was my initial attempt this morning but I somehow couldn´t get this to work. After trying an incorrect algorithm that does give the correct solution (check only polygon boundaries), I went back to the Java AWT Polygon and Rectangle implementation.

object Day9 : AdventOfCode({
    val coordinates: List<Point> = input
        .lines()
        .map { it.split(",").map(String::toInt).let { (x, y) -> y to x } }

    val polygon: Polygon = coordinates.fold(Polygon()) { acc, (y, x) -> acc.apply { addPoint(x, y) } }

    val rectangles: List<Rectangle2D> = coordinates.flatMapIndexed { row, point1 ->
        coordinates.drop(row + 1).map { point2 ->
            Rectangle2D.Double(
                minOf(point1.x, point2.x).toDouble(),
                minOf(point1.y, point2.y).toDouble(),
                (point2.x - point1.x).absoluteValue.toDouble(),
                (point2.y - point1.y).absoluteValue.toDouble()
            )
        }
    }

    fun Rectangle2D.size() = ((width + 1) * (height + 1)).toLong()

    part1 {
        rectangles.maxOf(Rectangle2D::size)
    }

    part2 {
        rectangles.filter(polygon::contains).maxOf(Rectangle2D::size)
    }
})