(a), (c), and (d) seems to be about exposing the algorithm's state and a function that performs a single step of the algorithm, rather than about having a class

(a), (c), and (d) seems to be about exposing the algorithm's state and a function that performs a single step of the algorithm, rather than about having a class. (b) seems like quite a bit of trouble, since the clone function must either copy the underlying graph by default or provide a mechanism for swapping out the underlying graph that fixes up the internal map of (node->distance) and the internal priority queue to refer to things in the new graph.