input: Write a python function to remove duplicate words from a string.
  assert remove_duplicates("I love coding love coding Python") == "I love coding Python"
  assert remove_duplicates("hello hello world") == "hello world"
  assert remove_duplicates("test test test this function function") == "test this function"
output: def remove_duplicates(s: str) -> str:
      words = s.split()
      seen = set()
      result = []
      for word in words:
          if word not in seen:
              seen.add(word)
              result.append(word)
      return ' '.join(result)