Homework 7: due 24 November, 5pm

1.) Modify the bfs code from lecture 23 so that bfs is a single function 
that takes a graph and a starting node and returns the traversal list.  
(i.e. remove global variables and put the supporting functions inside of 
the bfs function).

2.) Modify your resulting code to produce a shortest-path algorithm that 
takes a graph and a starting point and returns a list of pairs ( 
(v0,d0),(v1,d1)...) where the vi's are the nodes that are reachable from 
the starting point and the di's are the number of hops it takes to reach 
the vi's.