List with foldRight and match

object Raindrops {

  private val drops = List((3, "Pling"), (5, "Plang"), (7, "Plong"))

  def convert(n: Int): String =
    drops.foldRight(List[String]())((factor_drop, acc) =>
      if (n % factor_drop._1 == 0) factor_drop._2 :: acc else acc
    ) match {
      case drops if !drops.isEmpty => drops.mkString
      case _                       => n.toString()
    }
}

This approach starts by defining a List of tuples with numbers for the divisors and strings for the sounds. The foldRight() method is initialized with an empty List for its output and is called on the List of drops. Each tuple is passed to the lambda, where the input number is tested to be evenly divisible by number in the tuple.

Those tuple numbers by which the input number can be evenly divided have their strings prepended to the output List with the cons operator (::). When foldRight() is finished, its output List is passed to the match, where the List is checked for being empty. If not empty, then the mkString method is used to return the List elements as a String from the convert() method.

Otherwise, if the List is empty, then the match returns the original number as a String from the convert() method.