it.scala

val arg1 = Iterator(2, 3, 4, 8, 9,  12, 14, 17)
val arg2 = Iterator(1, 2, 3, 4, 6, 8, 9, 10, 11, 12, 13, 14, 17)
//??(arg1, arg2)=> Iterator((2, 4), (8, 9), (12, 12),(14, 17))

case class CeRange(start:Int, end:Option[Int]) {
  def passed(br: Int) = {
    end.map(br < _).getOrElse(true)
  }
}

def mkRanges(substrate:Iterator[Int]):Iterator[CeRange] = {
  val bufit = substrate.buffered
  Iterator.continually(bufit.hasNext).takeWhile(identity).map(_ => {
      val x = bufit.next()
      if (bufit.hasNext) CeRange(x, Some(bufit.head))
      else CeRange(x, None)
  })
}

def breakRanges(origin: Iterator[CeRange],
                breaks:Iterator[Int]):Iterator[CeRange] = {
  val bufbreaks = breaks.buffered
  origin.map(r => {
    Iterator.continually(bufbreaks.hasNext).takeWhile(_ && bufbreaks.head <= r.start).foreach(_ =>bufbreaks.next)
    if (bufbreaks.hasNext && r.passed(bufbreaks.head)) {
      r.copy(end = Some(bufbreaks.next()))
    }
    else r
  })
}


def mergeRanges(origin: Iterator[CeRange]):Iterator[CeRange] = {
  val bufit = origin.buffered
  Iterator.continually(bufit.hasNext).takeWhile(identity).map(_ => bufit.next).
    scanLeft(Right(CeRange(0, None)):Either[CeRange, CeRange])(
    (record, curr) => {
      if (bufit.hasNext && bufit.head.start == curr.end.get) Left({
        record.left.toOption.map(_.copy(end = curr.end)).getOrElse(curr)
      })
      else Right(
        record.left.toOption.map(identity).getOrElse(CeRange(curr.start, Some(curr.start)))
      )
    }).drop(1).collect{case Right(r) => r}
}

mergeRanges(breakRanges(mkRanges(arg1), arg2)).foreach(println)