Yandex interview algo task: find longest ascending/descending segment of an array

solution.dart

/*
Дан массив чисел a_1, a_2, ..., a_n .
Необходимо найти монотонный подотрезок (то есть строго убывающий или строго возрастающий) максимальной длины и
вернуть пару индексов его начала и конца.
*/

void main() {
  final tests = [
    [1, 1], // -> {1, 3}
    [2, 7, 5, 4, 4, 3], // -> {1, 1} or {0, 0}
    [2, 2, 2, 1, 1, 3], // -> {2, 3} or {4, 5}
    [1, 2, 3, 4, 5, 6, 7, 8, 9], // -> {0, 8}
    [1, 2, 3, 4, 3, 2, 1, 8, 9, 10, 11], // -> {6, 10}
    [1, 2, 3, 3, 3, 2, 3, 4, 5, 6, 8, 9, 10, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1], // -> {13, 23}
  ];
  
  for (final test in tests) {
    print(
      solution(test).answerString,
    );
  }
}

class Segment {
  final int start;
  final int end;
  int get length => end - start + 1;
  final bool isAscending;

  const Segment({
    required this.start,
    required this.end,
    this.isAscending = true,
  });

  Segment copyWith({
    int? start,
    int? end,
    bool? isAscending,
  }) =>
      Segment(
        start: start ?? this.start,
        end: end ?? this.end,
        isAscending: isAscending ?? this.isAscending,
      );

  String get answerString => '{$start, $end}';
}

Segment solution(final List<int> input) {
  assert(input.isNotEmpty, 'input must contain elements');
  Segment answer = Segment(start: 0, end: 0);
  Segment currentSegment = Segment(start: 0, end: 0);

  for (int i = 1; i < input.length; i++) {
    bool equalNumbers = input[i] == input[currentSegment.end];
    bool resetSegment = equalNumbers ||
        (input[i] < input[currentSegment.end]
            ? currentSegment.isAscending
            : !currentSegment.isAscending);

    if (resetSegment && currentSegment.length > answer.length) {
      answer = currentSegment;
    }
    currentSegment = Segment(
      start: resetSegment
          ? equalNumbers
              ? i
              : currentSegment.end
          : currentSegment.start,
      end: i,
      isAscending: input[i] > input[currentSegment.end],
    );
  }

  if (currentSegment.length > answer.length) answer = currentSegment;
  return answer;
}