Aoc2021-day8.scala

package lascala.aoc2021.day1_10.day8

opaque type Digit = Set[Char]
opaque type SignalPattern = Set[Digit]

def parse(s: String): (SignalPattern, Seq[Digit]) =
  val Array(pattern, digits) = s.split(" \\| ")
  def parsePart(s: String): Seq[Digit] =
    s.split(" ").map(_.toSet).toSeq
  (parsePart(pattern).toSet, parsePart(digits))

def recognize(pattern: SignalPattern): Map[Digit, Int] =
  val group = pattern.groupBy(_.size)
  val one = group(2).head
  val seven = group(3).head
  val four = group(4).head
  val eight = group(7).head

  val three = group(5).filter(one forall _.contains).head
  val five = group(5).filter(_ forall six.contains).head
  val two = (group(5) - three - five).head
  
  val six = group(6).filterNot(one forall _.contains).head
  val nine = group(6).filter(four forall _.contains).head
  val zero = (group(6) - six - nine).head
  Map(
    zero -> 0,
    one -> 1,
    two -> 2,
    three -> 3,
    four -> 4,
    five -> 5,
    six -> 6,
    seven -> 7,
    eight -> 8,
    nine -> 9,
  )

def decode(s: String): Int =
  val (pattern, digits) = parse(s)
  val map = recognize(pattern)
  digits.map(map).mkString.toInt

def solve1(s: String): BigInt =
  val target = Set(2, 3, 4, 7)
  val lines = s.split("\n")
  lines.map(parse).map{
    case (_, digits) =>
      digits.count{ (d: Digit) =>
        target contains d.size
      }
  }.sum
end solve1

def solve2(s: String): BigInt =
  val lines = s.split("\n")
  lines.map(decode).sum
end solve2

@main def part1: Unit =
  val ans = solve1(input)
  println(ans)

@main def part2: Unit =
  val ans = solve2(input)
  println(ans)

//val input =

Aoc2021-day8Test.scala

package lascala.aoc2021.day1_10.day8

import minitest.SimpleTestSuite
import hedgehog.minitest.HedgehogSupport
import hedgehog.*

object Day8Test extends SimpleTestSuite with HedgehogSupport:

  val testInput = """be cfbegad cbdgef fgaecd cgeb fdcge agebfd fecdb fabcd edb | fdgacbe cefdb cefbgd gcbe
edbfga begcd cbg gc gcadebf fbgde acbgfd abcde gfcbed gfec | fcgedb cgb dgebacf gc
fgaebd cg bdaec gdafb agbcfd gdcbef bgcad gfac gcb cdgabef | cg cg fdcagb cbg
fbegcd cbd adcefb dageb afcb bc aefdc ecdab fgdeca fcdbega | efabcd cedba gadfec cb
aecbfdg fbg gf bafeg dbefa fcge gcbea fcaegb dgceab fcbdga | gecf egdcabf bgf bfgea
fgeab ca afcebg bdacfeg cfaedg gcfdb baec bfadeg bafgc acf | gebdcfa ecba ca fadegcb
dbcfg fgd bdegcaf fgec aegbdf ecdfab fbedc dacgb gdcebf gf | cefg dcbef fcge gbcadfe
bdfegc cbegaf gecbf dfcage bdacg ed bedf ced adcbefg gebcd | ed bcgafe cdgba cbgef
egadfb cdbfeg cegd fecab cgb gbdefca cg fgcdab egfdb bfceg | gbdfcae bgc cg cgb
gcafb gcf dcaebfg ecagb gf abcdeg gaef cafbge fdbac fegbdc | fgae cfgab fg bagce"""

  example("day8 - solve1") {
    solve1(testInput) ==== 26
  }

  example("day8 - decode") {
    val line = "acedgfb cdfbe gcdfa fbcad dab cefabd cdfgeb eafb cagedb ab | cdfeb fcadb cdfeb cdbaf"
    decode(line) ==== 5353
  }

  example("day8 - solve2") {
    solve2(testInput) ==== 61229
  }

end Day8Test