Using directed graphs vs. undirected graphs.   Know when to use each. This should be fairly natural. For example, you'd use an undirected graph to represent friend connections between Facebook users, and a directed graph to represent following connections on Twitter.

BFS and DFS are directed graph algorithms.   Many canonical unweighted digraph problems (e.g. shortest paths and reachability) can be solved using code that is effectively identical to code for solving problems on unweighted graphs.

Importan digraph graph traversals.

Topological sort.

Recommended Problems

C level

  1. Fall 2012 Final, #3
  2. Spring 12 final, #3a, #3b
  3. Spring 14 Final, #2b

B level

  1. Spring 14 Final, #2a
  2. Using the previous problem, provide a topological sort that is different than the reverse postorder. If no such sort exists, explain why. Answers
  3. Textbook: 4.2.10, 4.2.20

A level

  1. Spring 2012 Final, #12
  2. 4.2.19, 4.2.22
  3. 4.2.27
  4. 4.2.40

Just for fun

  1. Write code similar to (or copy) the web crawler shown in lecture.