romanNumerals.scala

object RomanNumerals {
  val digitsToNumerals = Map(
    1 -> "I",
    5 -> "V",
    10 -> "X",
    50 -> "L",
    100 -> "C",
    500 -> "D",
    1000 -> "M"
  )

  def convert(int: Int): String =
    digitsToNumerals
      .toSeq                  // convert to sequence so we can sort
      .sortWith(_._1 > _._1)  // sort high to low by key
      .foldLeft(int -> "") {  // reduce (int, "") with the map to (0, numerals)
        case ((remain, numerals), (digit, numeral)) => // pattern match to destructure inputs
          (remain % digit, numerals + numeral * (remain / digit)) // divide remain by digit, build result, shrink remain
      }._2                    // return the numeral
}