gistfile1.txt

  def connections(from: Station, to: Station, departureTime: Time): Set[Seq[Hop]] = {
    require(from != to)

    def connections(from: Station, departureTime: Time, visitedStations: Set[Station]): Set[Seq[Hop]] =
      {
        val hopsFrom: Set[Hop] = hops.getOrElse(from, Set[Hop]())
        hopsFrom.filter(hop => hop.departureTime >= departureTime)
          .filterNot(hop => visitedStations.contains(hop.to))
          .flatMap(hop =>
            if (hop.to == to) Set(Seq[Hop](hop))
            else
              connections(hop.to, hop.arrivalTime, visitedStations + hop.from).map(seq => hop +: seq))
      }
    connections(from, departureTime, Set(from))
  }
}