Advent of Code 2022-9.scala

import java.io.FileInputStream
import scala.annotation.{tailrec, targetName}
import scala.io.StdIn

case class Point(x: Int, y: Int) {
  def +(that: Point): Point = Point(this.x + that.x, this.y + that.y)

  def moved(direction: Char): Point = direction match {
    case 'U' => this + Point(0, 1)
    case 'D' => this + Point(0, -1)
    case 'R' => this + Point(1, 0)
    case 'L' => this + Point(-1, 0)
  }
}

case class World(points: Vector[Point])
case class Command(direction: Char, steps: Int)

def simulate(acc: Vector[World], commands: Vector[Command]): Vector[World] =
  commands.headOption match
    case Some(command) =>
      val nextCommand: Vector[Command] = if 1 < command.steps then
        Vector(Command(command.direction, command.steps - 1)) ++ commands.tail
      else
        commands.tail

      val world = acc.last
      val movedHead = world.points.head.moved(command.direction)
      val nextPoints = world.points.tail.foldLeft(Vector(movedHead)) { (acc, tail) =>
        val head = acc.last

        val xDiff = (head.x - tail.x).abs
        val yDiff = (head.y - tail.y).abs
        if 1 >= xDiff && 1 >= yDiff then
          acc :+ tail
        else
          val nextTail = tail + Point((head.x - tail.x) / (1 max xDiff), (head.y - tail.y) / (1 max yDiff))
          acc :+ nextTail
      }
      simulate(acc :+ World(nextPoints), nextCommand)
    case _ =>
        acc

def solve9_1(commands: Vector[Command]): Int =
  val world = World(Vector.fill(2)(Point(0, 0)))
  simulate(Vector(world), commands).map(_.points.last).distinct.size


def solve9_2(commands: Vector[Command]): Int =
  val world = World(Vector.fill(10)(Point(0, 0)))
  simulate(Vector(world), commands).map(_.points.last).distinct.size



@main def solve9(): Unit =
  val in = new FileInputStream("example9-2.in")
  System.setIn(in)
  val inputs = Iterator.continually(StdIn.readLine())
    .takeWhile(line => null != line)
    .map(line => {
      val Array(direction, steps) = line.split(" ")
      Command(direction.head, steps.toInt)
    })
    .toVector
  println(solve9_1(inputs))
  println(solve9_2(inputs))