input: Write a python function to capitalize the last word of a given string.
  assert capitalize_last_word("hello world") == "hello World"
  assert capitalize_last_word("python is great") == "python is Great"
  assert capitalize_last_word("this is a test case") == "this is a test Case"
output: def capitalize_last_word(s):
      words = s.split()
      if words:
          words[-1] = words[-1].capitalize()
      return ' '.join(words)