Deduplicate the Activity Feed

Intermediate

An activity feed sometimes logs the same action twice in a row, but the display should show each action once, in the order it first occurred.

Implement `solve(List<String> input)` to return each value once in first-seen order.

Examples

Input["b", "a", "b", "c", "a", "d"]

Output["b", "a", "c", "d"]

Input["x", "x"]

Output["x"]

Hints

Track seen values in a Set; only add to the result list when first seen.

Anonymous Apex

List<String> solve(List<String> input) {
    // return each value once, first-seen order
    return null;
}

Your code runs in a secure sandbox against multiple hidden test cases. The problem is solved only when every test passes. Each run is isolated and any data changes are rolled back automatically.