input: Write a python function to group words of the same length together.
  assert group_words(["apple", "banana", "cherry", "date", "egg", "fig", "grape"]) == {5: ["apple"], 6: ["banana", "cherry"], 4: ["date"], 3: ["egg", "fig"], 5: ["grape"]}
  assert group_words(["cat", "dog", "elephant", "fox", "goat"]) == {3: ["cat", "dog", "fox"], 8: ["elephant"], 4: ["goat"]}
  assert group_words([""]) == {0: [""]}
  assert group_words(["a", "b", "cc", "dd", "eee", "fff"]) == {1: ["a", "b"], 2: ["cc", "dd"], 3: ["eee", "fff"]}
output: def group_words(words):
      word_dict = {}
      for word in words:
          length = len(word)
          if length not in word_dict:
              word_dict[length] = []
          word_dict[length].append(word)
      return word_dict