aoc2023/Day1.scala

package aoc.day1

import aoc._

// Part 1

def literalDigits(s: String) =
  s.toSeq.filter(_.isDigit).map(v => (v - '0').toInt)

def getValue(toDigits: String => Seq[Int])(s: String): Int =
  val digits = toDigits(s)
  digits.head * 10 + digits.last

def getSum(toDigits: String => Seq[Int]) =
  val values =
    lines.map(getValue(toDigits))
  println(values.sum)

// Part 2

val englishDigits =
  Seq("one", "two", "three", "four", "five", "six", "seven", "eight", "nine")

def literalOrEnglishDigits(s: String) =
  @scala.annotation.tailrec
  def loop(idx: Int, accum: Seq[Int]): Seq[Int] =
    if idx < 0 then accum
    else if s(idx).isDigit then loop(idx - 1, (s(idx) - '0').toInt +: accum)
    else
      val toMatch = s.slice(idx, idx + 5 /* enough to match english */ )
      val digit = englishDigits.indexWhere(toMatch.startsWith _)
      val nAccum = if digit == -1 then accum else (digit + 1) +: accum
      loop(idx - 1, nAccum)
  loop(s.length() - 1, Seq.empty)

@main def Day1(part: Int) = part match
  case 1 => getSum(literalDigits)
  case 2 => getSum(literalOrEnglishDigits)