code: def remove_redundancies(levels):
      
      seen = []
      final = []
      for line in levels:
          new_line = []
          for item in line:
              if item not in seen:
                  seen.append(item)
                  new_line.append(item)
          final.append(new_line)
      return final
docs: There are repeats in the output from get_levels(). We
      want only the earliest occurrence (after it's reversed)