code: public List<Trip> getDistinctTripsForStop (String stop_id) {
          return getStopTimesForStop(stop_id).stream()
                  .map(stopTime -> this.trips.get(stopTime.trip_id))
                  .distinct()
                  .collect(Collectors.toList());
      }
docs: Get list of distinct trips (filters out multiple visits by a trip) a given stop_id.