Advent of Code 24.scala

import java.io.FileInputStream
import collection.immutable.HashMap
import scala.annotation.tailrec
import scala.io.StdIn

val directionCodes = Vector(("e", 2, 0), ("se", 1, -1), ("sw", -1, -1), ("w", -2, 0), ("nw", -1, 1), ("ne", 1, 1))

case class Point(x: Int = 0, y: Int = 0):
  def move(dx: Int, dy: Int): Point =
    Point(x + dx, y + dy)

case class Directions(directions: String):
  def point(): Point =
    @tailrec
    def _point(codes: String, acc: Point): Point =
      directionCodes.find(code => codes.startsWith(code._1)) match
        case Some((word, dx, dy)) =>
          _point(codes.drop(word.length), acc.move(dx, dy))
        case _ =>
          acc
    _point(directions, Point())

def blackTilesFromInput(inputs: Vector[String]): Set[Point] = {
  inputs.foldLeft(Set[Point]()) { (acc, x) =>
    val point = Directions(x).point()
    if acc.contains(point) then
      acc - point
    else
      acc + point
  }
}

def adjacentWhiteTiles(blacks: Set[Point]): Set[Point] = {
  blacks.flatMap(point => directionCodes.map(code => point.move(code._2, code._3))).diff(blacks)
}

def numbefOfAdjacentBlack(blacks: Set[Point], point: Point): Int = {
  directionCodes.map(code => point.move(code._2, code._3)).count(blacks.contains)
}

def solve24_1(inputs: Vector[String]): Int = {
  blackTilesFromInput(inputs).size
}

def simulateDay(remainDay: Int, blacks: Set[Point]): Int = {
  if 0 >= remainDay then
    blacks.size
  else
    val whites = adjacentWhiteTiles(blacks)
    val newBlacks = whites.filter(white => 2 == numbefOfAdjacentBlack(blacks, white))
    val nextBlacks = blacks.filter(black => Set(1, 2).contains(numbefOfAdjacentBlack(blacks, black))) ++ newBlacks
    simulateDay(remainDay - 1, nextBlacks)
}

def solve24_2(inputs: Vector[String]): Int = {
  val blacks = blackTilesFromInput(inputs)
  simulateDay(100, blacks)
}

@main def solve24() =
  val in = new FileInputStream("example24-1.in")
  System.setIn(in)
  val inputs = Iterator.continually(StdIn.readLine())
    .takeWhile(line => null != line && line.trim.nonEmpty)
    .toVector
  println(solve24_1(inputs)) // 388
  println(solve24_2(inputs)) // 4002