P04.scala

object P04 {
  def groupIndexed[T](ts: Seq[(T, Int)]): Map[T, Seq[Int]] = {
    val (toMap, size) = convertToMapAndSize(ts)
    toMap.map {
      case (t, seq) =>
        val range = (1 to size).map(i => if (seq.contains(i)) 1 else 0)
        (t, range)
    }
  }

  private def convertToMapAndSize[T](ts: Seq[(T, Int)]) = ts.foldLeft((Map.empty[T, Set[Int]], 1)) {
    case ((map, max), (t, v)) =>
      val a = map.getOrElse(t, Set.empty[Int])
      (map + (t -> (a + v)), max.max(v))
  }
}