No README file = no partial credit for unfinished labs. If you cannot
get your output correct please tell the TAs what you think you have done
correctly and what you think you have not done correctly. You can get
partial credit for printing out a correct critical path length and/or
a topologically sorted set of tasks on the critical path(s).

--- correct, topologically-ordered set of
     tasks on the critical path               : up to -30
--- critical path length                      : up to -25
--- slack times 			      : up to -30
--- appropriate data structure for vertices   : up to -5

code style:
--- inadequate error messages                 : up to -10
--- hard coding constants		      : up to -5
--- commenting				      : up to -10
--- code organization and clarity	      : up to -15