Day 1: Secret Entrance

Mix.install([{:kino, "~> 0.11.3"}])

Day 01

• Puzzle: https://adventofcode.com/2025/day/1
• Input: https://adventofcode.com/2025/day/1/input

sample_input = Kino.Input.textarea("Paste Sample Input")

real_input = Kino.Input.textarea("Paste Real Input")

defmodule Password do
  def calculate_one(input) do
    input
    |> Kino.Input.read()
    |> String.split("\n", trim: true)
    |> Enum.reduce({0, 50}, fn instruction, {count, dial} ->
      change =
        case instruction do
          "L" <> amount -> -String.to_integer(amount)
          "R" <> amount -> String.to_integer(amount)
        end

      new_dial = normalize(dial + change)
      new_count = if new_dial == 0, do: count + 1, else: count
      {new_count, new_dial}
    end)
  end

  def calculate_two(input) do
    input
    |> Kino.Input.read()
    |> String.split("\n", trim: true)
    |> Enum.reduce({0, 50}, fn instruction, {count, dial} ->
      change =
        case instruction do
          "L" <> amount -> -String.to_integer(amount)
          "R" <> amount -> String.to_integer(amount)
        end

      {new_dial, zero_click_count} = apply_change(dial, change)
      new_count = if new_dial == 0, do: count + zero_click_count + 1, else: count + zero_click_count
      IO.puts("#{instruction} to #{new_dial} passing 0 #{new_count - count} times")
      {new_count, new_dial}
    end)
  end

  defp normalize(dial) when dial < 0, do: normalize(dial + 100)
  defp normalize(dial) when dial > 99, do: rem(dial, 100)
  defp normalize(dial), do: dial

  # I hate all the special cases here!!!
  defp apply_change(dial, change, carry \\ 0)
  defp apply_change(0, change, carry) when change < 0 do
    apply_change(100, change, carry)
  end
  defp apply_change(dial, change, carry) when change + dial < 0 do
    apply_change(dial, change + 100, carry + 1)
  end
  defp apply_change(dial, change, carry) when change + dial == 100 do
    {0, carry}
  end
  defp apply_change(dial, change, carry) when change + dial > 99 do
    apply_change(dial, change - 100, carry + 1)
  end
  defp apply_change(dial, change, carry), do: {dial + change, carry}
end

Password.calculate_one(sample_input)

Password.calculate_one(real_input)

Password.calculate_two(sample_input)

Password.calculate_two(real_input)