input: Write a function to implement an autocomplete system that predicts words based on the input text. The function should generate word candidates, filter them, rank them, and return the top 5 words. If the input text is empty or if there are no valid candidates, the function should return an empty list.
  assert autocomplete("hel") == ["hello", "help", "helm", "helpful", "hell"]
  assert autocomplete("a") == ["and", "about", "above", "across", "after"]
  assert autocomplete("") == []
  assert autocomplete("nonexistent") == []
  assert autocomplete("a long input text") == []
output: def autocomplete(input_text):
      word_candidates = ["hello", "help", "helm", "helpful", "hell", "and", "about", "above", "across", "after"]
      if not input_text:
          return []
      filtered_candidates = [word for word in word_candidates if word.startswith(input_text)]
      if not filtered_candidates:
          return []
      filtered_candidates.sort()
      return filtered_candidates[:5]