snippet.rb

require "rubygems"
require "gratr"
require "gratr/dot"

# 1 -> 2 -> 3
# |-> 6 -> |-> 4 -> 5 -> 2
# 2 -> 4 -> 5
    
dg = GRATR::Digraph[1,2, 2,3, 2,4, 4,5, 6,4, 1,6]

module GRATR
  class Digraph
    
    # Crappy n*n
    def find_cycle(from=self)
      return [] unless cyclic?
      cyclic_cycle = []
      forward_edge = Proc.new {|e| }
      back_edge    = Proc.new do |b| 
        cyclic_cycle = dfs_tree_from_vertex(b)
      end
      from.dfs({ 
       :forward_edge  => forward_edge,
       :back_edge    => back_edge
      })
      cyclic_cycle
    end
    
  end
end

# p dg.find_cycle
dep = 2
r = 5
existing_connections = dg.adjacent(dep)
p existing_connections
existing_connections.each {|c| dg.remove_edge!(r, c) }

dg.add_edge!(dep, r, dep)

existing_connections.each {|c| dg.add_edge!(dep, c) }

dg.write_to_graphic_file("png", "/tmp/graph")

`open /tmp/graph.png`