Read section 9.3.2 of the textbook (Weiss 3rd ed.) and complete the implementation
of dijkstra_shortest_paths in graphs/Algorithms.java. There are two helper
functions that you may use: initialize_single_source and relax_edge.
Also, there is a heap (priority queue) implementation in sequences/UpdatingHeap.java
that you may use.
In StudentTest.java, the testDijkstraSeven method corresponds
to Figure 9.20 in the textbook and is a good place to start debugging.