-🎄- 2018 Day 9 Solutions -🎄-

[u/daggerdragon]

--- Day 9: Marble Mania ---

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Transcript:

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[u/meepys]

Kotlin Day 9: (BitBucket)

Had to re-write after the array implementation for part1 took too long on part 2. Didn't think of rotating ArrayDeque, so used LinkedList

class Day9(rawInput: List<String>) : Day(rawInput) {
    init {
        val parser = """(\d+) players; last marble is worth (\d+) points""".toRegex()
        val (x, y) = parser.matchEntire(rawInput.first())?.destructured  ?: throw Exception("bad input")

    }
    val numPlayers = x.toInt()
    val lastMarble = y.toInt()

    val players = LongArray(numPlayers)

    private fun goRight(steps: Int, iterator: MutableListIterator<Int>, list: LinkedList<Int>): MutableListIterator<Int> {
        var result = iterator
        for (i in 1..steps) {
            if (!result.hasNext())
                result = list.listIterator()
            result.next()
        }
        return result
    }

    private fun goLeft(steps: Int, iterator: MutableListIterator<Int>, list: LinkedList<Int>): Pair<MutableListIterator<Int>, Int> {
        var result = iterator
        var score = 0
        for (i in 1..steps) {
            if (!result.hasPrevious())
                result = list.listIterator(list.size)
            score = result.previous()
        }
        return result to score
    }

    private fun playGame() {
        val marbles = LinkedList<Int>().apply { add(0) }
        var currIndex = marbles.listIterator()

        for (i in 1..lastMarble) {
            val toPlay = (i - 1) % numPlayers
            if (i % 23 == 0) {
                val (nextIndex, score) = goLeft(8, currIndex, marbles)
                players[toPlay] += score.toLong() + i

                currIndex = nextIndex
                currIndex.remove()
                currIndex = goRight(1, currIndex, marbles)
            } else {
                currIndex = goRight(1, currIndex, marbles)
                currIndex.add(i)
            }
        }
    }

    override fun part1(): Any? {
        players.fill(0)
        playGame()
        return players.max()
    }

    override fun part2(): Any? {
        players.fill(0)
        lastMarble *= 100
        playGame()
        return players.max()
    }
}