Day 5

Mix.install([
  {:aoc2024, path: (["."])}
])

Section

sample = """
47|53
97|13
97|61
97|47
75|29
61|13
75|53
29|13
97|29
53|29
61|53
97|53
61|29
47|13
75|47
97|75
47|61
75|61
47|29
75|13
53|13

75,47,61,53,29
97,61,53,29,13
75,29,13
75,97,47,61,53
61,13,29
97,13,75,29,47
"""

input = AoC2024.load_text("priv/day5.txt")

Part 1

defmodule Part1 do
  def parse(str) do
    [rules_str, updates_str] = String.split(str, "\n\n")

    rules = AoC2024.parse(rules_str, fn {str, _} -> String.split(str, "|") end)
    updates = AoC2024.parse(updates_str, fn {str, _} -> {str, String.split(str, ",")} end)

    {rules, updates}
  end

  def valid_update?({str, list}, rules) do
    Enum.all?(list, &validator(&1, str, rules))
  end

  defp validator(number, str, rules) do
    [left_list, right_list] =
      str |> String.split(number) |> Enum.map(&String.split(&1, ",", trim: true))

    Enum.all?(left_list, fn l_number ->
      Enum.find(rules, &(&1 == [l_number, number]))
      end) &&
      Enum.all?(right_list, fn r_number ->
        Enum.find(rules, &(&1 == [number, r_number]))
      end)
  end
end

{rules, updates} =
  sample
  |> Part1.parse()

updates
|> Enum.filter(&Part1.valid_update?(&1, rules))
|> Enum.map(fn {_, list} ->
  middle_index = div(length(list), 2)

  list
  |> Enum.at(middle_index)
  |> String.to_integer()
end)
|> Enum.sum()

{rules, updates} =
  input
  |> Part1.parse()

updates
|> Enum.filter(&Part1.valid_update?(&1, rules))
|> Enum.map(fn {_, list} ->
  middle_index = div(length(list), 2)

  list
  |> Enum.at(middle_index)
  |> String.to_integer()
end)
|> Enum.sum()

Part 2

defmodule Part2 do
  def fix_list(list, rules) do
    Enum.sort(list, &Enum.any?(rules, fn rule -> rule == [&1, &2] end))
  end
end

{rules, updates} =
  sample
  |> Part1.parse()

updates
|> Enum.reject(&Part1.valid_update?(&1, rules))
|> Enum.map(fn {_, list} ->
  middle_index = div(length(list), 2)

  list
  |> Part2.fix_list(rules)
  |> Enum.at(middle_index)
  |> String.to_integer()
end)
|> Enum.sum()

{rules, updates} = 
  input
  |> Part1.parse()

updates
|> Enum.reject(&Part1.valid_update?(&1, rules))
|> Enum.map(fn {_, list} ->
  middle_index = div(length(list), 2)

  list
  |> Part2.fix_list(rules)
  |> Enum.at(middle_index)
  |> String.to_integer()
end)
|> Enum.sum()