public int compare(Station arg0, Station arg1) {
if (arg0.getDistanceFromSource() > arg1.getDistanceFromSource()) {
return 1;
} else {
return -1;
}
}
private void relax(Station station) {
for (Station neighbor : station.getDestinations()) {
if (!visited.contains(neighbor)) {
int currentKnownDistance = getCurrentKnownDistance(station, neighbor);
if (neighbor.getDistanceFromSource() > currentKnownDistance) {
neighbor.setDistanceFromSource(currentKnownDistance);
unvisited.add(neighbor);
}
}
}
}
private void relaxRoundTrip(Station station, Station destination) {
for (Station neighbor : station.getDestinations()) {
if (!visited.contains(neighbor)) {
int currentKnownDistance = getCurrentKnownDistance(station, neighbor);
// to allow round trip if the neighbor is the destination, add
// it back to the queue
if (neighbor.getDistanceFromSource() > currentKnownDistance
|| neighbor.equals(destination)) {
neighbor.setDistanceFromSource(currentKnownDistance);
unvisited.add(neighbor);
}
}
}
}
public int findShortestTrip(Station from, Station to) {
initialize();
unvisited.add(from);
from.setDistanceFromSource(0);
while (!unvisited.isEmpty()) {
Station closest = unvisited.poll();
if (closest.equals(to)) {
return closest.getDistanceFromSource();
}
visited.add(closest);
relax(closest);
}
throw new MissingRouteException("Missing connection: " + from + " - " + to);
}
public int findShortestRoundTrip(Station from) {
initialize();
unvisited.add(from);
from.setDistanceFromSource(0);
// to allow round trip, for the first iteration skip 'are we there yet'
// check and don't add station to visited
boolean start = true;
while (!unvisited.isEmpty()) {
Station closest = unvisited.poll();
if (!start && closest.equals(from)) {
return closest.getDistanceFromSource();
}
if (!start) {
visited.add(closest);
}
relaxRoundTrip(closest, from);
start = false;
}
throw new MissingRouteException("Missing round connection: " + from);
}
private void initializeDistances() {
for (Station station : stations) {
station.setDistanceFromSource(Integer.MAX_VALUE);
}
}
private int getCurrentKnownDistance(Station current, Station neighbor) {
return current.getDistanceFromSource() + current.getDistanceTo(neighbor.getId());
}
