Discussion on: AoC Day 23: Experimental Emergency Teleportation

[Neil Gall]

Yesterday's was tough and if I'm honest I'm getting tired. So it was nice to find a straightforward part 1 at least.

Model

Simple stuff, we've done this many times already.

data class Pos(val x: Int, val y: Int, val z: Int)

data class Nanobot(val pos: Pos, val radius: Int)

typealias Manhattan = Int

operator fun Pos.minus(other: Pos): Manhattan = 
    Math.abs(x - other.x) + Math.abs(y - other.y) + Math.abs(z - other.z)

Parser

I've used parser combinators on nearly 2 out of 3 days this year, and I'm not going to stop now! At this point I'm writing them without requiring much reference to the documentation.

fun parse(input: String): List<Nanobot> {
    val integer = or(
        string("-").next(INTEGER).map { s -> -s.toInt() },
        INTEGER.map(String::toInt)
    )

    val pos = sequence(string("pos=<").next(integer),
                       string(",").next(integer),
                       string(",").next(integer).followedBy(string(">")),
                       ::Pos)

    val nanobot = sequence(pos, string(", r=").next(integer), ::Nanobot)

    return nanobot.sepBy(WHITESPACES).parse(input.trim())
}

Part 1

Easy stuff.

fun part1(nanobots: List<Nanobot>): Int {
    val strongest = nanobots.maxBy { n -> n.radius }!!
    return nanobots.count { n -> (strongest.pos - n.pos) <= strongest.radius }
}

Part 2

Oh wow, another doozy. I'll get back to you on this one!

[Ryan Palo]

Yeah you’ve definitely stuck with it. Nice job! 👍🏻