Day03

Setup

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

sample_text = Kino.Input.textarea("sample")

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

sample = Kino.Input.read(sample_text)
input = Kino.Input.read(input_text)

defmodule Shared do
  def parse(text) do
    text
    |> String.split("\n", trim: true)
    |> Enum.map(fn line ->
      line
      |> String.graphemes()
      |> Enum.map(fn
        "." -> 0
        "#" -> 1
      end)
    end)
  end

  def access(map, down, right) do
    max_right = map |> Enum.at(0) |> Enum.count()

    map
    |> Enum.at(down)
    |> Enum.at(rem(right, max_right))
  end

  def crawl(map, down, right), do: crawl(map, down, right, Enum.count(map), 0, 0)
  defp crawl(_map, down, _right, max, n, sum) when n * down >= max, do: sum

  defp crawl(map, down, right, max, n, sum) do
    val = access(map, down * n, right * n)
    crawl(map, down, right, max, n + 1, sum + val)
  end
end

part a

input
|> Shared.parse()
|> Shared.crawl(1, 3)

part b

map = input |> Shared.parse()

[{1, 1}, {1, 3}, {1, 5}, {1, 7}, {2, 1}]
|> Enum.reduce(1, fn {down, right}, acc -> acc * Shared.crawl(map, down, right) end)