Let's say, we have a relay race. Each member of the team runs their own path, passing the stick to the next member of the team. I have class, that describes track number (each team has own track number) and two names. The first name is stick's owner for part of track N and the second name is stick's owner for next part of the track (N+1).
class StickTransfer {
int trackId;
String stickFrom;
String stickTo;
}
My task is to sort all the StickTransfer's objects by 1) tracked 2) In order of stick's travel.
E.g. Let's say there is a team on track 1 with Alex -> John -> Smith -> Adam.
list.add(new StickTransfer(1, "John", "Smith");
list.add(new StickTransfer(1, "Alex", "John");
list.add(new StickTransfer(1, "Smith", "Adam");
order(list)
// After that I want to get:
// Alex - John - first entry
// John - Smith - second entry
// Smith - Adam - third entry
So, at first I deсided to use Java's sorting with such kind of comparator:
Comparator.comparing(StickTransfer::getTrackId)
.thenComparing((o1, o2) -> {
if (o1.getStickFrom().equals(o2.getStickTo())) {
return 1;
}
if (o1.getStickTo().equals(o2.getStickFrom())) {
return -1;
}
return 0;
});
But I got a problem, that with this comparator some of the entries are still unsorted. I think that's because it's not really a good comparator.
Now I have some questions:
1) Is it possible to write a right comparator for standard java sort method?
2) If not, is there a way to resolve this problem with some of Java standard methods?
3) Is there a name for such algorithmic problem?
Example of wrong sorting: Right order: X -> Y -> A -> B -> C -> D -> E
StickTransfer stickTransferArr[] = {
new StickTransfer(1, "A", "B"),
new StickTransfer(1, "C", "D"),
new StickTransfer(1, "B", "C"),
new StickTransfer(1, "X", "Y"),
new StickTransfer(1, "Y", "A"),
new StickTransfer(1, "D", "E")
};
Arrays.sort(stickTransferArr, cmp);
Result:
[{track=1, [A - > B]}, {track=1, [B - > C]}, {track=1, [C - > D]}, {track=1, [X - > Y]}, {track=1, [Y - > A]}, {track=1, [D - > E]}]
