What is the number of back edges during the above DFS traversal on G?

Consider the following graph G.

Modified DFS on G applied as follows: 
• Starting vertex is ‘p’. 
• Vertex is visited based on alphabetic order. 
• Vertices are visited in order p, q, r, s, t, v
• It works same as DFS except the visiting order restriction

What is the number of back edges during the above DFS traversal on G?

a. 2

b. 3

c. 4

d. 5

How to solve this type of problem..

1Comment
Sumit Verma @sumitkgp
13 Feb 2017 05:37 pm

Please understand the three basic definitions,
Back edges point from a node to one of its ancestors in the DFS tree.
Forward edges point from a node to one of its descendants.
Cross edges point from a node to a previously visited node that is neither an ancestor nor a descendant.