Advent of Code 2022

Mix.install([
  {:req, "~> 0.3.2"}
])

Day 8

input =
  "https://adventofcode.com/2022/day/8/input"
  |> Req.get!(headers: [cookie: "session=#{System.get_env("AOC_COOKIE")}"])
  |> Map.get(:body)

sample = """
30373
25512
65332
33549
35390
"""

lines =
  input
  |> String.split("\n", trim: true)
  |> Enum.map(fn line ->
    String.split(line, "", trim: true)
    |> Enum.map(&String.to_integer/1)
  end)

height_map =
  for {line, y} <- Enum.with_index(lines),
      {n, x} <- Enum.with_index(line),
      into: %{},
      do: {{x, y}, n}

Part 1

height_map
|> Enum.filter(fn {{x, y}, h} ->
  {x, y} |> IO.inspect()

  [
    {1, 0},
    {-1, 0},
    {0, 1},
    {0, -1}
  ]
  |> Enum.any?(fn {dx, dy} ->
    Stream.iterate(0, &(&1 + 1))
    |> Enum.reduce_while({{x, y}, h}, fn _i, {{x0, y0}, h0} ->
      c = {x0 + dx, y0 + dy}

      case Map.get(height_map, c) do
        nil ->
          {:halt, true}

        h1 when h1 < h0 ->
          {:cont, {c, h}}

        _ ->
          {:halt, false}
      end
    end)
    |> case do
      true -> true
      false -> false
      _ -> false
    end
  end)
end)
|> Enum.count()

Part 2

height_map
|> Enum.map(fn {{x, y}, h} ->
  {x, y} |> IO.inspect()

  [
    {1, 0},
    {-1, 0},
    {0, 1},
    {0, -1}
  ]
  |> Enum.map(fn {dx, dy} ->
    Stream.iterate(0, &(&1 + 1))
    |> Enum.reduce_while({{x, y}, h, 0}, fn _i, {{x0, y0}, h0, n} ->
      c = {x0 + dx, y0 + dy}

      case Map.get(height_map, c) do
        nil ->
          {:halt, n}

        h1 when h1 < h0 ->
          {:cont, {c, h0, n + 1}}

        _ ->
          {:halt, n + 1}
      end
    end)
    |> case do
      {_, _, n} -> n
      n -> n
    end
  end)
  |> Enum.reduce(&amp;(&amp;1 * &amp;2))
end)
|> Enum.max()