mygist.scala

object MyTest {
  def main(args: Array[String]): Unit = {
    println(sequence1(Seq(Some(1), None, Some(2), None)))
    println(sequence2(Seq(Some(1), Some(3), Some(2), Some(5))))
  }

  def sequence1[T](items: Seq[Option[T]]): Option[Seq[T]] = {
    items.foldLeft(Option(Seq[T]())) { (res, e) =>
      e match {
        case Some(value) => Option(res.getOrElse(Seq[T]()) :+ value)
        case None        => None
      }
    }
  }

  def sequence2[T](items: Seq[Option[T]]): Option[Seq[T]] = {
    var ns = Seq[T]()
    var state = false

    items.takeWhile {
      case None => {
        state = true
        false
      }
      case Some(n) => {
        ns = ns :+ n
        true
      }
    }

    if (!state) Some(ns)
    else None
  }

  def sequence3[T](items: Seq[Option[T]]): Option[Seq[T]] = {
    try {
      items.foldLeft(Option(Seq[T]())) { (res, e) =>
        e match {
          case Some(value) => Option(res.getOrElse(Seq[T]()) :+ value)
          case None        => throw new Exception("reached where it shouldn't")
        }
      }
    } catch {
      case _: Throwable => None
    }
  }
  
  def sequence4[T](items: Seq[Option[T]]): Option[Seq[T]] = {
    try {
      val ns = items.map {
        case Some(n) => n
        case _       => throw new Exception("stop me :))")
      }
      Some(ns)
    } catch {
      case _: Throwable => None
    }
  }

}