undirected_graph.rb

require 'tsort'

class UndirectedGraph < Hash
  include TSort

  def initialize(size, edges)
    super().tap do |hash|
      (1..size).each { |i| hash[i] = [] }

      edges.each do |(a, b)|
        hash[a] << b
        hash[b] << a
      end
    end
  end
  
  alias_method :tsort_each_node, :each_key
  
  def tsort_each_child(node, &block)
    fetch(node).each(&block)
  end
end

UndirectedGraph.new(4, [[1, 2], [1, 3]]).strongly_connected_components
# => [[1, 2, 3], [4]]