Drop the repeats
A feed sometimes sends the same id twice, and a clean list keeps only the first sighting.
- Keep the first occurrence of each value and drop any that repeat later.
- The relative order of the kept values is untouched.
dedupe(values: 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> dedupe(List<Integer> values) {
}Worked examples
| Call | Result |
|---|---|
dedupe(Main.<Integer>ls(1, 2, 3, 1, 2)) | Main.<Integer>ls(1, 2, 3) |
dedupe(Main.<Integer>ls(1, 1, 1)) | Main.<Integer>ls(1) |
dedupe(Main.<Integer>ls()) | Main.<Integer>ls() |
dedupe(Main.<Integer>ls(3, 1, 2, 1, 3)) | Main.<Integer>ls(3, 1, 2) |
Hint
Carry a set of what you have already seen, and only push a value the first time you meet it.
Reference solution in Java
List<Integer> dedupe(List<Integer> values) {
Set<Integer> seen = new HashSet<>();
List<Integer> result = new ArrayList<>();
for (int v : values) {
if (seen.add(v)) result.add(v);
}
return result;
}