// Find the route with matching last station name and extend with new station name.
public List <Route> SpawnMatchedRoute(List <Route> possibleRoutes, string prevStationName, Station stationToAdd, int duration)
{
List <Route> newRoutes = new List <Route>();
foreach (Route route in possibleRoutes)
{
if (route.LastStation.Station.StationName == prevStationName)
{
Route updatedRoute = (Route)route.Clone();
updatedRoute.AddStationToRoute(stationToAdd);
updatedRoute.AddTotalDuration(duration);
newRoutes.Add(updatedRoute);
}
}
return(newRoutes);
}
public List <Route> FindKShortestPath(string sourceStationName, string destStationName, int k)
{
List <Route> kRoutes = new List <Route>();
Queue <Station> stationQueue = new Queue <Station>();
HashSet <string> visitedStationName = new HashSet <string>();
Station curStation = Stations[sourceStationName];
stationQueue.Enqueue(curStation);
List <Route> possibleRoutes = new List <Route>();
Route startRoute = new Route();
startRoute.AddStationToRoute(curStation);
possibleRoutes.Add(startRoute);
visitedStationName.Add(curStation.StationName);
bool foundKRoutes = false;
while (stationQueue.Count > 0 && !foundKRoutes)
{
curStation = stationQueue.Dequeue();
List <Route> updatedRoutes = new List <Route>();
foreach (StationEdge stationEdge in curStation.ConnectedStations)
{
Station connectedStation = stationEdge.Station;
//valid route found.
if (connectedStation.StationName == destStationName && kRoutes.Count < k)
{
List <Route> validRoutes = SpawnValidRoute(possibleRoutes, curStation.StationName, connectedStation, stationEdge.Duration);
int availableRouteSlots = k - kRoutes.Count < validRoutes.Count ? k - kRoutes.Count : validRoutes.Count;
for (int i = 0; i < availableRouteSlots; i++)
{
kRoutes.Add(validRoutes[i]);
possibleRoutes.Remove(validRoutes[i]);
}
if (kRoutes.Count >= k)
{
foundKRoutes = true;
break;
}
continue;
}
if (!visitedStationName.Contains(connectedStation.StationName))
{
visitedStationName.Add(curStation.StationName);
stationQueue.Enqueue(connectedStation);
updatedRoutes.AddRange(SpawnMatchedRoute(possibleRoutes, curStation.StationName, connectedStation, stationEdge.Duration));
}
}
if (updatedRoutes.Count > 0)
{
updatedRoutes.AddRange(SpawnMismatchedRoute(possibleRoutes, curStation.StationName));
possibleRoutes = updatedRoutes;
}
}
kRoutes = kRoutes.OrderBy(route => route.TotalDuration).ToList();
return(kRoutes);
}
