topo_sort.rb

# Topological sort
Do a DFS and push items in a queue as you traverse the leaf nodes adding deepest element first
Queue will hold sorted output (for dependency management)
graph = {0 => [1], 1 => [2,3], 2 => [3], 3 => []}
def topo_sort(graph)
	seen = Set.new
	queue = []
	graph.each do |node, v|
	  dfs_helper(graph, node, seen, visited)
	end
	queue.inspect
end

def dfs_helper(graph, node, seen, queue)
  return if seen.include?(node)
  seen.add(node)
  graph[node].each do |child|
    dfs_helper(child)
  end
  q.push(node)
end