Superfluous :GRAY assignment in depth first visit?

[delphaber]

Hello!

Isn't line 200 superfluous? We are already marking the vertex as :GRAY in line 192 when we go deeper in the recursion level at line 201.

Just wondering if I'm missing something :)

rgl/lib/rgl/traversal.rb

Lines 191 to 201 in 3cdf5c2

	def depth_first_visit(u, vis = DFSVisitor.new(self), &b)
	vis.color_map[u] = :GRAY
	vis.handle_examine_vertex(u)
	each_adjacent(u) do |v|
	vis.handle_examine_edge(u, v)
	if vis.follow_edge?(u, v) # (u,v) is a tree edge
	vis.handle_tree_edge(u, v) # also discovers v
	vis.color_map[v] = :GRAY # color of v was :WHITE
	depth_first_visit(v, vis, &b)

[monora]

On line 192 vertex u is marked :GRAY, whereas on line 200 vertex v, which is adjacent to u is also marked :GRAY, because the edge (u,v) shall be followed (vis.follow_edge(u, v) is true).

[delphaber]

Thanks for the answer but I still don't get it, sorry 😅
Vertex v passed to the block in line 195 will become vertex u when calling depth_first_visit recursively in line 201, and it will be coloured (again) to :GRAY in line 192.

[monora]

You are right! Thank you for this thorough code review! Deleting this 10 year old line does not break the tests! Issue #66 will fix it.

[delphaber]

Good! My graph teory study is rusty so I was not sure if I was missing something! Thanks for this gem!