get_families: (Dict[str, List[str]]) -> Dict[str, List[str]]
Return a “last name to first names” dictionary based on the given “person to friends” dictionary. The returned dictionary should contain every person whose name appears in the given dictionary (as a key or in a value list). The keys in the returned dictionary should be the last names of people in the given dictionary. (Remember: every person has exactly one last name.) The values are lists of the first names (in alphabetical order) of people with a given last name. Names in the list should be unique: no one should be listed more than once. Use the
