intToEnglish.scala

val toEnglish = Map((0, 4) -> "four", (1, 3) -> "thirty", (2, 2) -> "two hundreds", (3, 1) -> "one thousand")

def intToEnglish(a: Int): String = a.toString.toList
  .map { _.toString.toInt }
  .reverse.zipWithIndex.reverse
  .map { t => toEnglish(t.swap) }
  .mkString(" ")

intToEnglish(4)    // res0: String = four
intToEnglish(34)   // res1: String = thirty four
intToEnglish(234)  // res2: String = two hundreds thirty four
intToEnglish(1234) // res3: String = one thousand two hundreds thirty four