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>
C# 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
public List<int> Dedupe(List<int> values) {
}Worked examples
| Call | Result |
|---|---|
Dedupe(new List<int> { 1, 2, 3, 1, 2 }) | new List<int> { 1, 2, 3 } |
Dedupe(new List<int> { 1, 1, 1 }) | new List<int> { 1 } |
Dedupe(new List<int> { }) | new List<int> { } |
Dedupe(new List<int> { 3, 1, 2, 1, 3 }) | new List<int> { 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 C#
public List<int> Dedupe(List<int> values) {
var seen = new HashSet<int>();
var result = new List<int>();
foreach (var v in values) {
if (seen.Add(v)) result.Add(v);
}
return result;
}