Day09AllInASingleNight.kt

package adventofcode.year2015

import adventofcode.Puzzle
import adventofcode.PuzzleInput
import adventofcode.common.Permutations.permutations

class Day09AllInASingleNight(customInput: PuzzleInput? = null) : Puzzle(customInput) {
    override val name = "All in a Single Night"

    private val distances by lazy {
        input
            .lines()
            .associate {
                val (cityA, cityB, distance) = INPUT_REGEX.find(it)!!.destructured
                setOf(cityA, cityB) to distance.toInt()
            }
    }

    private val cities by lazy { distances.keys.flatten().toSet() }

    private val routes by lazy {
        cities
            .permutations()
            .map { route ->
                route.dropLast(1).foldIndexed(0) { index, distance, _ ->
                    distance + distances[setOf(route[index], route[index + 1])]!!
                }
            }
    }

    override fun partOne() = routes.minOrNull() ?: 0

    override fun partTwo() = routes.maxOrNull() ?: 0

    companion object {
        private val INPUT_REGEX = """(\w+) to (\w+) = (\d+)""".toRegex()
    }
}