2.exs

defmodule Checksum do
  def countchars(''), do: 0

  def countchars(chars) do
    chars
    |> Enum.uniq()
    |> Enum.map(&countchar(&1, chars))
  end

  def countchar(_, []), do: 0

  def countchar(char, [h | t]) do
    ((char == h && 1) || 0) + countchar(char, t)
  end

  def checksum(lines) when is_list(lines) do
    {c1, c2} =
      lines
      |> Enum.map(&(String.to_charlist(&1) |> countchars()))
      |> Enum.map(fn c -> {(2 in c && 1) || 0, (3 in c && 1) || 0} end)
      |> Enum.reduce({0, 0}, fn {c1, c2}, {ch1, ch2} ->
        {c1 + ch1, c2 + ch2}
      end)

    c1 * c2
  end

  def checksum(line) do
    line |> String.to_charlist() |> List.wrap()
  end
end

defmodule Chars do
  def detect_similar(list, d \\ 0)
  def detect_similar([], _), do: []

  def detect_similar([l1 | t], d) do
    Enum.map(t, fn l2 -> similar(l1, l2) |> elem(1) end) |>
    Enum.find(fn x -> x end) || detect_similar(t, d + 1)
  end

  def detect_similar(_, _), do: []

  def similar(a, b, c \\ {0, []})
  def similar(_, _, {nr, _}) when nr > 1, do: {nr, false}
  def similar([], [], r), do: r
  def similar([], _, r), do: r
  def similar(_, [], r), do: r

  def similar([c1 | t1], [c1 | t2], {nr, s}) do
    similar(t1, t2, {nr, [c1 | s]})
  end

  def similar([_c1 | t1], [_c2 | t2], {nr, s}) do
    similar(t1, t2, {nr + 1, s})
  end
end

# ["aabbbcccde", "aabc", "aaabc", "abab"] |> Checksum.checksum() |> IO.inspect()

File.read("2.txt")
|> elem(1)
|> String.split()
|> Checksum.checksum()
|> IO.puts()

File.read("2.txt")
|> elem(1)
|> String.split()
|> Enum.map(&String.to_charlist(&1))
|> Chars.detect_similar()
|> Enum.reverse()
|> IO.inspect()