code: def _ending_consonants_only(self, letters: List[str]) -> List[int]:
          
          reversed_letters = list(reversed(letters))
          length = len(letters)
          for idx, letter in enumerate(reversed_letters):
              if not self._contains_vowels(letter) and self._contains_consonants(letter):
                  return [(length - idx) - 1]
              if self._contains_vowels(letter):
                  return []
              if self._contains_vowels(letter) and self._contains_consonants(letter):
                  return []
          return []
docs: Return a list of positions for ending consonants.