Collapse repeats in a sorted feed
A sorted export repeats an id whenever a row was touched twice. The importer wants each id once, still in order.
- The input arrives sorted ascending, so equal values are always adjacent.
- Each distinct value survives once, in the order it first appeared.
- An empty feed comes back empty.
dedupeSorted(ids: list<int>) → list<int>
Java needs a compiler and Drill does not host one yet, so this page is the reference rather than an exercise: the problem, worked examples, and the solution in full. To type it out, the same problem runs in Python.
Where you start
List<Integer> dedupeSorted(List<Integer> ids) {
}Worked examples
| Call | Result |
|---|---|
dedupeSorted(Main.<Integer>ls(1, 1, 2, 3, 3, 3)) | Main.<Integer>ls(1, 2, 3) |
dedupeSorted(Main.<Integer>ls(1, 2, 3)) | Main.<Integer>ls(1, 2, 3) |
dedupeSorted(Main.<Integer>ls(5, 5, 5, 5)) | Main.<Integer>ls(5) |
dedupeSorted(Main.<Integer>ls()) | Main.<Integer>ls() |
Hint
Because it is sorted you only ever need to compare against the value you kept last. Walk forward and keep a value only when it differs from that one.
Reference solution in Java
List<Integer> dedupeSorted(List<Integer> ids) {
List<Integer> out = new ArrayList<>();
for (int id : ids) {
if (out.isEmpty() || out.get(out.size() - 1) != id) out.add(id);
}
return out;
}