ScalaBoi: A John Conway Puzzler - Part 1 of 2 - Oops, That Didn't Work! Why?!

TheTenDivisibilities.scala

//C1 - Initial Scala solution attempt

val lettersToDigitsPrefixSize = 3

val letterToDigits =
  List(
    'a' -> List(1, 3, 7, 9),
    'b' -> List(2, 4, 6, 8),
    'c' -> List(1, 3, 7, 9),
    'd' -> List(2, 4, 6, 8),
    'e' -> List(5),
    'f' -> List(2, 4, 6, 8),
    'g' -> List(1, 3, 7, 9),
    'h' -> List(2, 4, 6, 8),
    'i' -> List(1, 3, 7, 9),
    'j' -> List(0)
  )
val digitsByLetter =
  letterToDigits.toMap
val letters =
  letterToDigits.map(_._1)

def generateCandidates = {
  def recursive(remaining: List[(Char, List[Int])] = letterToDigits.take(lettersToDigitsPrefixSize), accumulator: List[Int] = List(0)): List[Int] =
    if (remaining.isEmpty || accumulator.isEmpty)
      accumulator
    else {
      val (letter, digits): (Char, List[Int]) = remaining.head
      val indexOfLetter: Int = letters.indexOf(letter) + 1
      val accumulatorNew: List[Int] =
        for {
          prior <- accumulator
          priorAsSetOfDigits = prior.toString.toSet[Char].map(_.asDigit)
          digit <- digits.filter(!priorAsSetOfDigits.contains(_))
          value = (prior * 10) + digit
          if (value % indexOfLetter) == 0
        } yield value
      recursive(remaining.tail, accumulatorNew)
    }
  recursive()
}

println(generateCandidates)