Lecture 01-25-17 (Digraphs)

Weak Connectivity

• Underlying undirected graph is connected

??? connectivity

• Won’t give name because there’s a homework problem on it
• For each pair of vertices, there is a path between them

Strong Connectivity

• for each pair of vertices, there is a path both ways
• Algorithm
  1. DFS on x to make sure can reach all
  2. Reverse graph (flip edges)
  3. Repeat step 1
• Testing with cross edges
  • Is LOW(x) < DFS#(x)
    • If not, break off strongly connected component

Strongly Connected Component Graph

• Has no cycles