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