Answer from cs61c-fz (Sean Nyberg 16014383) for Question 4
Yes, both methods will work. Since the structure is not circular, the reference count method works since it is possible to have 0 pointers pointing at the storage. Since the mark and sweep method will reclaim any structures not linked to the roots of the rest of the reachable objects, it works just as well as the reference count method for this particular structure.