Day5.scala

package sungkmi.aoc2020.day5

case class Seat(row: Int, column: Int)

extension (s: Seat):
  def id: Int = s.row * 8 + s.column

def parseSeat(s: String): Seat =
  val (rowString, columnString) = s splitAt 7
  def parseBinaryString(zero: Char, one: Char)(str: String): Int = BigInt(str.map{
    case c if c == zero => '0'
    case c if c == one => '1'
  }, 2).toInt

  val row = parseBinaryString('F', 'B')(rowString)
  val column = parseBinaryString('L', 'R')(columnString)
  Seat(row, column)

@main def part1: Unit =
  val ans = seats.map(_.id).max
  println(ans)

@main def part2: Unit =
  val ans = Range(55, 906) `diff` seats.map(_.id).sorted
  println(ans)

lazy val seatStrings: Seq[String] = input.split("\n").toSeq

lazy val seats: Seq[Seat] = seatStrings `map` parseSeat

// lazy val input = """ ... 

Day5Test.scala

package sungkmi.aoc2020.day5

class Day5Test extends munit.FunSuite {

  test("parse seat") {
    val s = "FBFBBFFRLR"
    val expected = Seat(44,5)

    assertEquals(parseSeat(s), expected)
  }

  test("seat id") {
    val s = "FBFBBFFRLR"
    val expected = 357

    assertEquals(parseSeat(s).id, expected)
  }
}