aoc2021 day 12

Setup

Mix.install([{:kino, "~> 0.4.1"}])

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

Section

inputs1 = """
start-A
start-b
A-c
A-b
b-d
A-end
b-end
"""

inputs2 = """
dc-end
HN-start
start-kj
dc-start
dc-HN
LN-dc
HN-end
kj-sa
kj-HN
kj-dc
"""

defmodule Recursion do
  def recur(_adj_map, "end", _visited_list), do: 1

  def recur(adj_map, current, visited_list) when length(visited_list) < 100 do
    next_cands = adj_map[current]

    next_cands
    |> Enum.filter(&amp;can_go?(&amp;1, visited_list))
    |> Enum.map(&amp;recur(adj_map, &amp;1, [current | visited_list]))
    |> Enum.sum()
  end

  defp can_go?("start", _visited_list), do: false

  defp can_go?(target, visited_list) do
    cond do
      String.upcase(target) == target ->
        true

      target not in visited_list ->
        true

      true ->
        false
    end
  end
end

adj_map =
  input
  |> Kino.Input.read()
  |> String.split(["\n", "-"], trim: true)
  |> Enum.chunk_every(2)
  |> Enum.reduce(%{}, fn [a, b], adj_map ->
    adj_map
    |> Map.update(a, [b], &([b] ++ &1))
    |> Map.update(b, [a], &([a] ++ &1))
  end)

Recursion.recur(adj_map, "start", [])

Part 2

defmodule Recursion2 do
  def recur(_adj_map, "end", visited_list, _) do
    # IO.inspect(visited_list)
    1
  end

  def recur(adj_map, current, visited_list, chance?) when length(visited_list) < 100 do
    next_cands = adj_map[current]

    next_cands
    |> Enum.filter(&amp;can_go?(&amp;1, visited_list, chance?))
    |> Enum.map(
      &amp;recur(adj_map, &amp;1, [current | visited_list], chance? &amp;&amp; !use_chance?(&amp;1, visited_list))
    )
    |> Enum.sum()
  end

  defp can_go?("start", _visited_list, _), do: false

  defp can_go?(target, visited_list, chance?) do
    cond do
      String.upcase(target) == target ->
        true

      target not in visited_list or chance? ->
        true

      true ->
        false
    end
  end

  defp use_chance?(target, visited_list) do
    String.downcase(target) == target and target in visited_list
  end
end

adj_map =
  input
  |> Kino.Input.read()
  |> String.split(["\n", "-"], trim: true)
  |> Enum.chunk_every(2)
  |> Enum.reduce(%{}, fn [a, b], adj_map ->
    adj_map
    |> Map.update(a, [b], &([b] ++ &1))
    |> Map.update(b, [a], &([a] ++ &1))
  end)

Recursion2.recur(adj_map, "start", [], true)