AoC Day 23: Experimental Emergency Teleportation

Ryan Palo on December 23, 2018

Day 23! Two days left until Christmas! We have now officially graduated from 2D coordinates, and we've got nanobots flying around in three dime... [Read Full]
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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!

 

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

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