Answer from cs61c-ao (Roger Tseng 16507336) for Question 4
yes this structure can be reclaimed by the reference count method because the first node does not contain a pointer to itself, thus when the reference count algorithm checks this node, it will see that it has no pointers to it and then free the node.

if the very top left node is the root node, then the rest of the nodes will not be reclaimed by the mark and sweep method because the algorithm will recognize that they are still in use.  however, if this structure is indpendent of any root pointers, the mark and sweep method will mark these nodes and garbage collect them when performing the sweep.