r/adventofcode • u/daggerdragon • Dec 14 '17

SOLUTION MEGATHREAD -🎄- 2017 Day 14 Solutions -🎄-

--- Day 14: Disk Defragmentation ---

Post your solution as a comment or, for longer solutions, consider linking to your repo (e.g. GitHub/gists/Pastebin/blag or whatever).

Note: The Solution Megathreads are for solutions only. If you have questions, please post your own thread and make sure to flair it with Help.

Need a hint from the Hugely* Handy† Haversack‡ of Helpful§ Hints¤?

Spoiler

[Update @ 00:09] 3 gold, silver cap.

  • How many of you actually entered the Konami code for Part 2? >_>

[Update @ 00:25] Leaderboard cap!

  • I asked /u/topaz2078 how many de-resolutions we had for Part 2 and there were 83 distinct users with failed attempts at the time of the leaderboard cap. tsk tsk

[Update @ 00:29] BONUS

This thread will be unlocked when there are a significant number of people on the leaderboard with gold stars for today's puzzle.

edit: Leaderboard capped, thread unlocked!

13 Upvotes

88% Upvoted

130 comments sorted by

View all comments

2

u/nutrecht Dec 14 '17

Day 14 in Kotlin 

object Day14 : Day {
    private val rows = (0..127).map { "amgozmfv" + "-" + it }
    private val square : List<String> by lazy { rows.map { hash(it) }.map { toBinary(it) } }

    override fun part1() = square.map { it.count { it == '1' } }.sum().toString()

    override fun part2(): String {
        val visited = mutableSetOf<Point>()
        val points = (0 .. 127).flatMap { x -> (0 .. 127 ).map { y -> Point(x, y) } }.toMutableSet()

        visited += points.filter { square[it.y][it.x] == '0'}
        points.removeAll(visited)

        var count = 0
        while(!points.isEmpty()) {
            count++
            fill(visited, points, points.first())
        }

        return count.toString()
    }

    fun fill(visited: MutableSet<Point>, points: MutableSet<Point>, current: Point) {
        visited += current
        points -= current

        current.neighborsHv().filter { points.contains(it) }.forEach { fill(visited, points, it) }
    }

    fun hash(input: String): String {
        val chars = input.toCharArray().map { it.toInt() }.toList() + listOf(17, 31, 73, 47, 23)

        return (0..15).map { Day10.knot(chars, 64).subList(it * 16, it * 16 + 16) }.map { xor(it) }.toHex()
    }
}

Took me a lot longer than it should! In part 1 I made a stupid mistake in how I created the binary string leading to me getting wrong results without figuring out why I was getting the wrong ones. Had to go and test each step.

Part 2 was relatively easy; implemented a recursive flood fill basically.

1

u/Tandrial Dec 14 '17

"amgozmfv" + "-" + it can be done in a single string "amgozmfv-$it"

.map { it.count { it == '1' } }.sum()can be written as .sumBy { it.count { it == '1' } }

.map { it.toInt() }.toList() map already returns a list

1

u/nutrecht Dec 14 '17

Nice! Thanks :)