Advent of Code 21.scala

import java.io.FileInputStream
import scala.io.StdIn

type Allergen = String
type Ingredient = String

case class FoodListElement(ingredient: Vector[Ingredient], allergen: Vector[Allergen]) {
  def allergenMap(): Map[Allergen, Set[Ingredient]] = {
    ingredient.foldLeft(Map[Allergen, Set[Ingredient]]()) { (acc, ingredient) =>
      allergen.foldLeft(acc) { (subAcc, allergen) =>
        subAcc.updated(allergen, subAcc.getOrElse(allergen, Set()) + ingredient)
      }
    }
  }
}

def removeRedundant(availables: Map[Allergen, Set[Ingredient]]): Map[Allergen, Set[Ingredient]] = {
  val determined = availables.filter(1 == _._2.size).map(_._2.toIterable.head).toSet
  val nextAvailables = availables.view.mapValues(v => {
    if 1 == v.size then
      v
    else
      v.filter(!determined.contains(_))
  }).toMap
  if availables == nextAvailables then
    availables
  else
    removeRedundant(nextAvailables)
}

def findAllergenIngredient(availables: Map[Allergen, Set[Ingredient]], unkowns: Vector[FoodListElement]): Map[Allergen, Ingredient] = {
  unkowns.headOption match {
    case Some(foodListElement) =>
      val allergens = foodListElement.allergenMap()
      val nextAvailables = allergens.foldLeft(availables) { (acc, kv) =>
        val newOnes = kv._2
        acc.updated(kv._1, acc.get(kv._1).map { _.intersect(newOnes) }.getOrElse(newOnes))
      }
      findAllergenIngredient(nextAvailables, unkowns.tail)
    case _ =>
      removeRedundant(availables).filter(1 == _._2.size).view.mapValues(_.toIterable.head).toMap
  }
}

def solve1(foodList: Vector[FoodListElement]): Int = {
  val allergens = findAllergenIngredient(Map(), foodList).values.toSet
  foodList.flatMap(_.ingredient).count(ingredient => !allergens.contains(ingredient))
}

def solve2(foodList: Vector[FoodListElement]): String = {
  val allergens = findAllergenIngredient(Map(), foodList).toVector
  allergens.sortBy(_._1).map(_._2).mkString(",")
}

@main def solve21() =
  val in = new FileInputStream("example21-1.in")
  System.setIn(in)

  val inputs = Iterator.continually(StdIn.readLine()).takeWhile(_ != null).toVector
  val foodList = inputs.map { line =>
    val worlds = line.split("[\\(\\)]").filter(_.nonEmpty)
    val ingredients = worlds.head.split(" ").filter(_.nonEmpty).toVector
    val allergens = worlds.last.split("[, ]").filter(_.nonEmpty).toVector.tail
    FoodListElement(ingredients, allergens)
  }
  println(solve1(foodList)) // 2517
  println(solve2(foodList)) // rhvbn,mmcpg,kjf,fvk,lbmt,jgtb,hcbdb,zrb