Multiplication of two state machines

sm.rb

a = {a: [:b, :c], b: [:c]}

def get_edges(sm)
	res = []
	sm.each do |s, e|
		e.each do |d|
			res.push([s,d])
		end
	end
	res
end

def get_nodes(sm)
	get_edges(sm).flatten.uniq
end

def get_starts(sm)
	get_nodes(sm) - get_edges(sm).collect(&:last)
end

b = {p: [:q]}

def multiply_starts(a,b)
	# starting nodes of the combined state machine
	get_starts(a).product(get_starts(b))
end

def multiply_traverse(a, b, ns)
	f = ns.first
	l = ns.last
	# puts "f = #{f}, l = #{l}"
	res = []
	a[f].to_a.each do |e|
		res.push([e,l])
	end
	b[l].to_a.each do |g|
		res.push([f,g])
	end
	res
end

def multiply(a,b)
	r = {}
	multiply_starts(a,b).each do |pair|
		r[pair] = multiply_traverse(a,b, pair)
	end
	r.values.flatten(1).each do |pair|
		next if pair.nil?
		r[pair] ||= multiply_traverse(a,b,pair)
	end
	return r
end