Day 01

Mix.install([
  {:kino, "~> 0.14"}
])

example_input =
  Kino.Input.textarea("example input:")
  |> Kino.render()

real_input = Kino.Input.textarea("real input:")

Common

defmodule AOC do
  def parse(input) do
    input
    |> Kino.Input.read()
    |> String.split("\n", trim: true)
    |> Enum.map(&String.split(&1, ~r/\s/, trim: true))
    |> Enum.reduce({[], []}, fn [left, right], {lefts, rights} ->
      {[String.to_integer(left) | lefts], [String.to_integer(right) | rights]}
    end)
  end
end

Part 1

defmodule Part1 do
  def process({lefts, rights}) do
    Enum.map([lefts, rights], &Enum.sort/1)
    |> Enum.zip_with(fn [left, right] -> abs(left - right) end)
    |> Enum.sum()
  end
end

real_input
|> AOC.parse()
|> Part1.process()

Part 2

defmodule Part2 do
  def process({lefts, rights}) do
    frequencies = Enum.frequencies(rights)

    lefts
    |> Enum.reduce(0, fn left, sum ->
      sum + left * Map.get(frequencies, left, 0)
    end)
  end
end

real_input
|> AOC.parse()
|> Part2.process()