Courses Algo Problem

courses.exs

defmodule Dag do
  defstruct edges: %{}

  def from_list(list) do
    Enum.reduce(list, %Dag{}, fn [to, from], dag -> insert(dag, from, to) end)
  end

  def insert(%Dag{edges: edges}, from, to) do
    nodes = Map.get(edges, from, [])
    updated_edges = Map.put(edges, from, [to | nodes])

    %Dag{edges: updated_edges}
  end

  def circular?(%Dag{edges: edges}) do
    Enum.any?(edges, fn {start, _} -> circular_check(MapSet.new(), [start], edges) end)
  end

  def output(list) do
    IO.inspect("Input: #{inspect(list)}")

    list
    |> Dag.from_list()
    |> Dag.circular?()
    |> (&IO.inspect("Output: #{!&1}")).()
  end

  defp circular_check(_seen, [], _edges) do
    false
  end

  defp circular_check(seen, [next | rest], edges) do
    MapSet.member?(seen, next) ||
      circular_check(MapSet.put(seen, next), rest ++ Map.get(edges, next, []), edges)
  end
end

Dag.output([[1, 0]])
Dag.output([[1, 0], [0, 1]])
Dag.output([[1, 0], [0, 2], [2, 3]])
Dag.output([[1, 0], [0, 2], [2, 3], [3, 4], [4, 5], [2, 3]])