Advent of Code 2021-13.scala

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

case class Point(x: Int, y: Int):
  def fold(axis: Char, v: Int): Point =
    axis match
      case 'x' =>
        copy(x = if v < x then v - (x - v) else x)
      case _ =>
        copy(y = if v < y then v - (y - v) else y)

def solve13_1(points: Vector[Point], folds: Vector[(Char, Int)]): Int =
  val (axis, v) = folds.head
  points.map(_.fold(axis, v)).toSet.size

def solve13_2(points: Vector[Point], folds: Vector[(Char, Int)]): String =
  val foldedPoints = folds.foldLeft(points)((acc, x) => acc.map(_.fold(x._1, x._2)))
  val dots = Array.fill[Char](foldedPoints.map(_.y).max + 1, foldedPoints.map(_.x).max + 1)(' ')
  val result = foldedPoints.foldLeft(dots)((acc, p) => acc.updated(p.y, acc(p.y).updated(p.x, '.')))
  result.map(_.mkString).mkString("\n")

@main def solve13(): Unit =
  val in = new FileInputStream("example13-2.in")
  System.setIn(in)
  val inputs = Iterator.continually(StdIn.readLine())
    .takeWhile(line => null != line && line.trim.nonEmpty)
    .map(_.split(','))
    .map { case Array(x, y) => Point(x.toInt, y.toInt) }
    .toVector
  val foldInputs = Iterator.continually(StdIn.readLine())
    .takeWhile(line => null != line && line.trim.nonEmpty)
    .map(_.split(' ').last.split("="))
    .map { case Array(x, y) => (x.toCharArray.head, y.toInt) }
    .toVector
  println(solve13_1(inputs, foldInputs))
  println(solve13_2(inputs, foldInputs))