input: Write a function to create 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 predicted words. If the input text is empty, return an empty list.
  assert autocomplete("hel")==['help', 'hello', 'hell', 'helmet', 'helpful']
  assert autocomplete("pro")==['program', 'project', 'programming', 'process', 'professional']
  assert autocomplete("un")==['understand', 'unknown', 'understanding', 'understandable', 'under']
  assert autocomplete("z")==['zero', 'zone', 'zip', 'zoo', 'zone']
  assert autocomplete("")==[]
output: def autocomplete(input_text):
      word_list = ['help', 'hello', 'hell', 'helmet', 'helpful', 'program', 'project', 'programming', 'process', 'professional', 'understand', 'unknown', 'understanding', 'understandable', 'under', 'zero', 'zone', 'zip', 'zoo']
      if not input_text:
          return []
      candidates = [word for word in word_list if word.startswith(input_text)]
      candidates.sort()
      return candidates[:5]