Day15ScienceForHungryPeople.kt

package adventofcode.year2015

import adventofcode.Puzzle
import adventofcode.PuzzleInput
import adventofcode.common.cartesianProduct
import kotlin.math.max

class Day15ScienceForHungryPeople(customInput: PuzzleInput? = null) : Puzzle(customInput) {
    override val name = "Science for Hungry People"

    private val ingredients by lazy { input.lines().map(Ingredient::invoke) }

    private val recipes by lazy {
        (1..ingredients.size)
            .map { (0..TABLESPOON_COUNT).toList() }
            .cartesianProduct()
            .filter { it.sum() == TABLESPOON_COUNT }
            .map { it.mapIndexed { index, amount -> ingredients[index] * amount } }
            .map { it.sum() }
    }

    override fun partOne() = recipes.maxOf(Ingredient::score)

    override fun partTwo() = recipes.filter { it.calories == CALORIE_COUNT }.maxOf(Ingredient::score)

    companion object {
        private val INPUT_REGEX = """capacity (-?\d+), durability (-?\d+), flavor (-?\d+), texture (-?\d+), calories (\d+)""".toRegex()

        private const val TABLESPOON_COUNT = 100
        private const val CALORIE_COUNT = 500

        private data class Ingredient(
            val capacity: Int,
            val durability: Int,
            val flavor: Int,
            val texture: Int,
            val calories: Int,
        ) {
            val score = max(0, capacity) * max(0, durability) * max(0, flavor) * max(0, texture)

            operator fun times(amount: Int) =
                Ingredient(amount * capacity, amount * durability, amount * flavor, amount * texture, amount * calories)

            operator fun plus(other: Ingredient) =
                Ingredient(
                    capacity + other.capacity,
                    durability + other.durability,
                    flavor + other.flavor,
                    texture + other.texture,
                    calories + other.calories,
                )

            companion object {
                operator fun invoke(input: String): Ingredient {
                    val (capacity, durability, flavor, texture, calories) =
                        INPUT_REGEX
                            .find(input)!!
                            .destructured
                            .toList()
                            .map(String::toInt)

                    return Ingredient(capacity, durability, flavor, texture, calories)
                }
            }
        }

        private fun Collection<Ingredient>.sum(): Ingredient = reduce { sum, summand -> sum + summand }
    }
}