aoc 2019 day 4

Setup

Mix.install([{:kino, "~> 0.5.0"}])

input = Kino.Input.textarea("input")

Part 1

defmodule Part1 do
  def solve(input) do
    input
    |> Kino.Input.read()
    |> String.split("-", trim: true)
    |> then(fn [left, right] -> String.to_integer(left)..String.to_integer(right) end)
    |> Enum.count(fn num ->
      num_str = to_string(num)

      cond do
        decrease?(num_str) -> false
        non_double?(num_str) -> false
        true -> true
      end
    end)
  end

  defp decrease?(<<h, b>>), do: h > b
  defp decrease?(<<h, b, _rest::binary>>) when h > b, do: true
  defp decrease?(<<_h, rest::binary>>), do: decrease?(rest)

  defp non_double?(""), do: true
  defp non_double?(<<h, h, _rest::binary>>), do: false
  defp non_double?(<<_h, rest::binary>>), do: non_double?(rest)
end

Part1.solve(input)

s = "12"

<<h, b, rest::binary>> = s

Part 2

defmodule Part2 do
  def solve(input) do
    input
    |> Kino.Input.read()
    |> String.split("-", trim: true)
    |> then(fn [left, right] -> String.to_integer(left)..String.to_integer(right) end)
    |> Enum.count(fn num ->
      num_str = to_string(num)

      cond do
        decrease?(num_str) -> false
        non_double?(num_str) -> false
        true -> true
      end
    end)
  end

  defp decrease?(<<h, b>>), do: h > b
  defp decrease?(<<h, b, _rest::binary>>) when h > b, do: true
  defp decrease?(<<_h, rest::binary>>), do: decrease?(rest)

  defp non_double?(""), do: true
  defp non_double?(<<x, x, x, x, x, rest::binary>>), do: non_double?(rest)
  defp non_double?(<<x, x, x, x, rest::binary>>), do: non_double?(rest)
  defp non_double?(<<x, x, x, rest::binary>>), do: non_double?(rest)
  defp non_double?(<<x, x, _rest::binary>>), do: false
  defp non_double?(<<_x, rest::binary>>), do: non_double?(rest)
end

Part2.solve(input)