1.exs

System.argv()
|> File.stream!([], 1)
|> Stream.with_index()
|> Enum.reduce_while([], fn {char, idx}, last_4 ->
  last_4 =
    last_4
    |> Enum.concat([char])
    |> Enum.slice(-4, 4)

  if last_4 |> Enum.uniq() |> Enum.count() == 4 do
    {:halt, idx + 1}
  else
    {:cont, last_4}
  end
end)
|> IO.inspect

2.exs

System.argv()
|> File.stream!([], 1)
|> Stream.with_index()
|> Enum.reduce_while([], fn {char, idx}, last_14 ->
  last_14 =
    last_14
    |> Enum.concat([char])
    |> Enum.slice(-14, 14)

  if last_14 |> Enum.uniq() |> Enum.count() == 14 do
    {:halt, idx + 1}
  else
    {:cont, last_14}
  end
end)
|> IO.inspect