Answer from cs61c-aj (Kevin Li 15855812) for Question 4
Yes for both. Reference works because this is not a circularly linked list and so therefore nothing is pointing to the first top left block and that has a reference of 0. It will get released. Then the number of pointers pointing to the top right and lower left will be reduced to 0. These two will also be released. Finally the lower right reference counter drops to 0 and therefore is released and the structure is reclaimed. Mark and Sweep will work because if no root is pointing to the structure then it is unmarked. If no root is pointing to any part of the structure then it is sweeped and reclaimed.