remove duplicate elements from a list.

// Challenge: remove duplicate elements from a list.
// Input: [1, 2, 2, 3, 3, 3, 4]
// Expected output: [1, 2, 3, 4]

// Solution 1: using a Set.
// A Set does not allow duplicates, so converting to a Set and back
// to a List removes them all at once. It's the most idiomatic way in Dart.
List<T> removeDuplicates<T>(List<T> list) {
  return list.toSet().toList();
}

// Solution 2: by hand, to explain the logic in an interview.
// We iterate and only add what we haven't seen yet.
List<T> removeDuplicatesManual<T>(List<T> list) {
  final seen = <T>{};
  final result = <T>[];
  for (final element in list) {
    if (!seen.contains(element)) {
      seen.add(element);
      result.add(element);
    }
  }
  return result;
}

void main() {
  print(removeDuplicates([1, 2, 2, 3, 3, 3, 4])); // [1, 2, 3, 4]
  print(removeDuplicates(['a', 'b', 'a', 'c'])); // [a, b, c]
  print(removeDuplicatesManual([1, 1, 1])); // [1]
  print(removeDuplicatesManual<int>([])); // [] (edge case)

  // Explanation:
  // The Set version is the shortest, but it doesn't guarantee order
  // in all cases (although in practice Dart keeps insertion order).
  // The manual version keeps the order explicitly and makes the "how" clear.
  // The <T> makes the functions generic: they work for lists of any type.
}