Inverse FizzBuzz by Scala

gistfile1.scala

object InverseFizzBuzz extends App {

  implicit def makeSeqSafer[A](xs: Seq[A]) = new {
    def safeMinBy[B](f: A => B)(implicit cmp: Ordering[B]) =
      if (xs.nonEmpty) Some(xs.minBy(f)) else None
  }
  
  def solve(words: Seq[String]): Option[(Int, Int)] = {
    List(3,5,6,9,10,12,15).flatMap { x =>
      val (subseq, pos) = Stream.from(x).collect {
        case i if i % 15 == 0 => ("fizzbuzz", i)
        case i if i %  3 == 0 => ("fizz", i)
        case i if i %  5 == 0 => ("buzz", i)
      }.take(words.length).toList.unzip

      if (subseq == words) Some(pos.head, pos.last) else None
    }.safeMinBy { case (s,e) => e - s }
  }


  assert( solve(Seq("fizz"))                 == Some(3,3) )
  assert( solve(Seq("buzz"))                 == Some(5,5) )
  assert( solve(Seq("fizz", "buzz"))         == Some(9,10) )
  assert( solve(Seq("buzz", "fizz"))         == Some(5,6) )
  assert( solve(Seq("fizz", "buzz", "fizz")) == Some(3,6) )
  assert( solve(Seq("fizz", "fizz"))         == Some(6,9) )
  assert( solve(Seq("fizz", "fizz", "buzz")) == Some(6,10) )
  assert( solve(Seq("fizzbuzz", "fizz"))     == Some(15,18) )
  assert( solve(Seq("fizzbuzz", "fizzbuzz")) == None )
}