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