Day Twenty

Mix.install([
  {:kino, "~> 0.7.0"}
])

Section

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

defmodule DayTwenty do
  def solve1(input) do
    input
    |> String.split("\n", trim: true)
    |> Enum.map(&String.to_integer/1)
    |> Enum.with_index()
    |> rotate()
    |> Enum.map(&elem(&1, 0))
    |> then(fn ls ->
      i = Enum.find_index(ls, fn i -> i == 0 end)

      (Enum.at(ls, rem(i + 1000, length(ls))) |> IO.inspect()) +
        (Enum.at(ls, rem(i + 2000, length(ls))) |> IO.inspect()) +
        (Enum.at(ls, rem(i + 3000, length(ls))) |> IO.inspect())
    end)
  end

  def solve2(input) do
    input
    |> String.split("\n", trim: true)
    |> Enum.map(&String.to_integer/1)
    |> Enum.map(fn x -> x * 811_589_153 end)
    |> Enum.with_index()
    |> then(fn ls ->
      Enum.reduce(1..10, ls, fn _, ls -> rotate(ls) end)
    end)
    |> Enum.map(&elem(&1, 0))
    |> then(fn ls ->
      i = Enum.find_index(ls, fn i -> i == 0 end)

      (Enum.at(ls, rem(i + 1000, length(ls))) |> IO.inspect()) +
        (Enum.at(ls, rem(i + 2000, length(ls))) |> IO.inspect()) +
        (Enum.at(ls, rem(i + 3000, length(ls))) |> IO.inspect())
    end)
  end

  defp rotate(ls) do
    rotate(ls, 0)
  end

  defp rotate(ls, i_to_move) do
    case Enum.find_index(ls, fn {_v, orig_i} -> i_to_move == orig_i end) do
      nil ->
        ls

      i ->
        {v, orig_i} = Enum.at(ls, i)
        ls = List.delete_at(ls, i)

        new_i =
          if v < 0 do
            rem(i + v, length(ls)) - 1
          else
            rem(i + v, length(ls))
          end

        ls = List.insert_at(ls, new_i, {v, orig_i})
        rotate(ls, i_to_move + 1)
    end
  end
end

DayTwenty.solve2(Kino.Input.read(input))