input: Write a function to sort words in a given string by their length in decreasing alphabetical order. If the given string is empty then return an empty string.
  assert sort_words_by_length_and_alphabet("This is the string which is to be sorted")=="string sorted which is the is This to be"
  assert sort_words_by_length_and_alphabet("apple banana cherry date")=="banana cherry apple date"
  assert sort_words_by_length_and_alphabet("")==""
output: def sort_words_by_length_and_alphabet(s):
      if not s:
          return ""
      words = s.split()
      words.sort(key=lambda x: (-len(x), x))
      return " ".join(words)