refactored

Plumber.ex

defmodule Plumber do
  def input(file) do
    file
    |> File.stream!()
    |> Enum.map(&(Regex.split(~r/\D+/, String.trim(&1))))
    |> Enum.reduce(%{}, fn([first | rest],acc) -> Map.put(acc,first,rest) end )
  end

  def count([], acc, input) do
    case Map.keys(input) do
      [first | _ ] -> count(Map.get(input,first,[]), acc + 1, Map.delete(input, first))
      [] -> acc
    end
  end
  def count([first | rest], acc, input) do
    queue = Map.get(input, first, []) |> Enum.filter(&(Map.has_key?(input,&1)))
    count(queue ++ rest, acc, Map.delete(input, first))
  end

  def howMany(file) do
    count([], 0, input(file))
  end
end