Advent of Code 2021-8.scala

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

case class Input(patterns: Vector[String], fourDigit: Vector[String])

def is1478(digit: String): Boolean =
  digit.length match
    case 2 | 4 | 3 | 7 =>
      true
    case _ =>
      false

def solve8_1(inputs: Vector[Input]): Int =
  inputs.map(input => input.fourDigit.count(is1478)).sum

def numberMap(input: Input): Map[Set[Char], Int] =
  val counts = "abcdefg".map(c => input.patterns.count(_.contains(c)) -> c).groupBy(_._1).view.mapValues(_.map(_._2).toSet).toMap
  val b = counts(6).head
  val e = counts(4).head
  val f = counts(9).head
  val number7 = input.patterns.find(_.length == 3).get.toSet
  val number1 = input.patterns.find(_.length == 2).get.toSet
  val a = number7.diff(number1).head
  val c = counts(8).diff(Set(a)).head
  val abcefSet = Set(a, b, c, e, f)
  val number0 = input.patterns.find(pattern => pattern.length == 6 && abcefSet.diff(pattern.toSet).isEmpty).head
  val g = number0.toSet.diff(abcefSet).head
  val d = counts(7).diff(Set(g)).head
  Map(
    Set(a, b, c, e, f, g) -> 0,
    Set(c, f) -> 1,
    Set(a, c, d, e, g) -> 2,
    Set(a, c, d, f, g) -> 3,
    Set(b, c, d, f) -> 4,
    Set(a, b, d, f, g) -> 5,
    Set(a, b, d, e, f, g) -> 6,
    Set(a, c, f) -> 7,
    Set(a, b, c, d, e, f, g) -> 8,
    Set(a, b, c, d, f, g) -> 9,
  )

def toNumber(numbers: Map[Set[Char], Int], text: String): Int =
  numbers(text.toSet)

def toNumber(numbers: Map[Set[Char], Int], texts: Vector[String]): Int =
  texts.foldLeft(0) { (acc, x) =>
    acc * 10 + toNumber(numbers, x)
  }

def solve8_2(inputs: Vector[Input]): Int =
  inputs.map { input =>
    toNumber(numberMap(input), input.fourDigit)
  }.sum

@main def solve8(): Unit =
  val in = new FileInputStream("example8-2.in")
  System.setIn(in)
  val inputs = Iterator.continually(StdIn.readLine())
    .takeWhile(line => null != line && line.trim.nonEmpty)
    .map(line => {
      val Array(patterns, fourDigit) = line.trim.split("\\|")
      Input(patterns.trim.split(" ").toVector, fourDigit.trim.split(" ").toVector)
    }).toVector
  println(solve8_1(inputs))
  println(solve8_2(inputs))