I'm working on a DFS of a directed graph, How do I get to a node without any edges pointed at it?

Question

http://homepage.cs.uiowa.edu/~hzhang/c31/ch09-probs.pdf

The problem is 9.2 in the PDF above. I am confused how I am to get to Node E because it only has edges pointed away from the node; None are pointed at Node E. I appreciate the help.

Answer 1

If you want to traverse all nodes by DFS, You must iterate for each node, and check the node is accessed or not, and use the node to begin a DFS.

    procedure DFS(G,v):
      label v as discovered
      for all edges from v to w in G.adjacentEdges(v) do
          if vertex w is not labeled as discovered then
              recursively call DFS(G,w)

    procedure traverse_by_DFS(G):
        for v in G:
            if v is dicovered:
                continue
            DFS(G, v)

Answer 2

It's a trick question. You don't hit node E, because you are forced to start at node A. This is the effect being given a starting node that isn't the true root - the result is an incomplete traversal.