Closed smithtim closed 5 years ago
You can use BFS or DFS graph iterator to get the answer:
require 'rgl/adjacency'
require 'rgl/traversal'
module RGL::Graph
def path?(v1, v2)
# create BFS Iterarator starting from v1
it = self.bfs_iterator(v1)
# Use method any? of Enumerable
it.any?(v2)
end
end
dg=RGL::DirectedAdjacencyGraph[1,2 ,2,3 ,2,4, 4,5, 6,4, 1,6]
dg.path?(1,5)
=> true
dg.path?(5,1)
=> false
Each GraphIterator is a Stream which implements Enumerable:
dg.bfs_iterator.class.ancestors
=> [RGL::BFSIterator, RGL::GraphVisitor, RGL::GraphIterator, RGL::GraphWrapper, Stream, Enumerable, Object, PP::ObjectMixin, Kernel, BasicObject]
@smithtim does my answer help you? Can we close the issue?
That helps, thanks!
If v1
is not in the graph, it throws an exception. This fixes that:
module RGL::Graph
def path?(v1, v2)
# avoid exception if v1 is not in the graph
return false if not self.has_vertex?(v1)
# create BFS Iterator starting from v1
it = self.bfs_iterator(v1)
# Use method any? of Enumerable
it.any?(v2)
end
end
I am surprised that path?
is not included in RGL::Graph
by default. Maybe it could be added?
I would not add the method to the basic Graph API, because:
You could add the method in this module extending module Graph. But that would also surprise people violating the POLS.
I would rather add the code either in README or examples.rb. What do you think?
I would be okay with having it in traversal.rb
. Maybe traversal.rb
could be renamed path.rb
? Or maybe it could go in its own module? Just throwing out some ideas. I do think it should be part of the library, rather than something people have to copy-paste.
I think we can put it in an own module path.rb
. Would you like to contribute it?
Hi @monora,
Please check my PRs, I've tried both approaches: simply added info to the README, created a method in path.rb
Is there a method to check whether a path exists between two vertices?
E.g.
graph.path? v1, v2