notes for hw7

[Jared Saia]

- I fixed some small typos on the hw, please download the new version

- Problem 3:Hint:  you only need to use the max-flow/min-cut theorem here.  There is no need to use induction.

- Problem 4: Hint: Set this up as a min-cut problem.  Classifying each vertex as foreground or background is equivalent to the vertex being on the s side or t side of the cut (in some new graph G')