input: def rotate_triples(s: str):
      """
      returns a string after rotating groups of three characters cyclically.
      """
      # Divide the string into groups of 3 characters each.
      groups = [s[(3 * i):min((3 * i + 3), len(s))] for i in range((len(s) + 2) // 3)]
      # Rotate characters within each group, unless the group has fewer than 3 characters.
      groups = [(group[1:] + group[0]) if len(group) == 3 else group for group in groups]
      return "".join(groups)
  
  
  def reverse_rotate_triples(s: str):
      """
      takes a string encoded with rotate_triples function and returns the decoded string.
      """
output:     # Divide the string into groups of 3 characters each.
      groups = [s[(3 * i):min((3 * i + 3), len(s))] for i in range((len(s) + 2) // 3)]
      # Reverse-rotate characters within each group, unless the group has fewer than 3 characters.
      groups = [(group[-1] + group[:-1]) if len(group) == 3 else group for group in groups]
      return "".join(groups)