Day21AllergenAssessment.kt

package adventofcode.year2020

import adventofcode.Puzzle
import adventofcode.PuzzleInput

class Day21AllergenAssessment(customInput: PuzzleInput? = null) : Puzzle(customInput) {
    private val foods by lazy { input.lines().map(Food::invoke) }

    override fun partOne(): Int {
        val ingredientsToAllergens = foods.ingredientsAllergensMap()

        return foods.flatMap(Food::ingredients).filter { !ingredientsToAllergens.contains(it) }.size
    }

    override fun partTwo() = foods.ingredientsAllergensMap().entries.sortedBy { it.value }.joinToString(",") { it.key }

    companion object {
        private data class Food(
            val ingredients: List<String>,
            val allergens: List<String>
        ) {
            companion object {
                operator fun invoke(input: String): Food {
                    val ingredients = input.split("(").first().trim().split(" ")
                    val allergens = when {
                        input.contains("(") -> input.split("(").last().replace("contains ", "").replace(")", "").split(", ")
                        else -> emptyList()
                    }

                    return Food(ingredients, allergens)
                }
            }
        }

        private fun List<Food>.ingredientsAllergensMap() = flatMap { food ->
            food.allergens.map { allergen ->
                food.ingredients.last { ingredient ->
                    filter { it.allergens.contains(allergen) }.all { it.ingredients.contains(ingredient) }
                } to allergen
            }
        }.toMap()
    }
}