```ruby
# frozen_string_literal: true

# Module for Annotations.
module HeadMusic::Style::Annotations; end

# A melodic line should have direction changes.
class HeadMusic::Style::Annotations::DirectionChanges < HeadMusic::Style::Annotation
  def marks
    return unless overage.positive?
    penalty_exponent = overage**0.5
    HeadMusic::Style::Mark.for_all(notes, fitness: HeadMusic::PENALTY_FACTOR**penalty_exponent)
  end

  private

  def overage
    return 0 if notes.length < 2
    [notes_per_direction - self.class.maximum_notes_per_direction, 0].max
  end

  def notes_per_direction
    notes.length.to_f / (melodic_intervals_changing_direction.length + 1)
  end

  def melodic_intervals_changing_direction
    melodic_intervals.each_cons(2).select do |interval_pair|
      interval_pair[0].direction != interval_pair[1].direction
    end
  end
end
```

Improve code style of iterator
user
```ruby
# frozen_string_literal: true

# Module for Annotations.
module HeadMusic::Style::Annotations; end

# A melodic line should have direction changes.
class HeadMusic::Style::Annotations::DirectionChanges < HeadMusic::Style::Annotation
  def marks
    return unless overage.positive?
    penalty_exponent = overage**0.5
    HeadMusic::Style::Mark.for_all(notes, fitness: HeadMusic::PENALTY_FACTOR**penalty_exponent)
  end

  private

  def overage
    return 0 if notes.length < 2
    [notes_per_direction - self.class.maximum_notes_per_direction, 0].max
  end

  def notes_per_direction
    notes.length.to_f / (melodic_intervals_changing_direction.length + 1)
  end

  def melodic_intervals_changing_direction
    melodic_intervals.each_cons(2).reject do |interval_pair|
      interval_pair[0].direction == interval_pair[1].direction
    end
  end
end
```
assistant