input: Write a function to determine if it is possible to get a given string in non-decreasing order by performing any number of alphabetical rotations on the given string. If it is possible return True else return False. If the given string is empty then return True.
  assert rotate_string("star") == False
  assert rotate_string("hello") == True
  assert rotate_string("world") == False
  assert rotate_string("abc") == True
  assert rotate_string("") == True
output: def rotate_string(s):
      if not s:
          return True
      for i in range(len(s)):
          if s[i:] + s[:i] == ''.join(sorted(s)):
              return True
      return False