Advent of Code 2022-5.scala

import java.io.FileInputStream
import scala.annotation.tailrec
import scala.io.StdIn

case class Command(from: Int, to: Int, value: Int)

@tailrec
def _step(crate: Vector[Vector[Char]], commands: Vector[Command], shouldReverse: Boolean): Vector[Vector[Char]] =
  commands.headOption match
    case None => crate
    case Some(command) =>
      val newCrate = crate.zipWithIndex.map { (c, i) =>
        if i == command.from then
          c.drop(command.value)
        else if i == command.to then
          if shouldReverse then
            crate(command.from).take(command.value).reverse ++ c
          else
            crate(command.from).take(command.value) ++ c
        else
          c
      }
      _step(newCrate, commands.tail, shouldReverse)

def solve5_1(crate: Vector[Vector[Char]], commands: Vector[Command]): String =
  _step(crate, commands, true).map(_.head).mkString("")

def solve5_2(crate: Vector[Vector[Char]], commands: Vector[Command]): String =
  _step(crate, commands, false).map(_.head).mkString("")

@main def solve5(): Unit =
  val in = new FileInputStream("example5-2.in")
  System.setIn(in)
  val crate = Iterator.continually(StdIn.readLine())
    .takeWhile(line => line.strip().nonEmpty)
    .map(_.toVector)
    .toVector
    .transpose
    .zipWithIndex
    .filter(_._2 % 4 == 1)
    .map(_._1.init.filter(x => x != ' '))

  val commands = Iterator.continually(StdIn.readLine())
    .takeWhile(line => null != line)
    .map(line => {
      val parts = line.split(" ")
      Command(parts(3).toInt - 1, parts(5).toInt - 1, parts(1).toInt)
    })
    .toVector

  println(solve5_1(crate, commands))
  println(solve5_2(crate, commands))