Advent of Code 2024 - Day 02

Mix.install([
  {:req, "~> 0.5"},
  {:benchee, "~> 1.3"}
])

Input

opts = [headers: [{"cookie", "session=#{System.fetch_env!("LB_AOC_SESSION")}"}]]
puzzle_input = Req.get!("https://adventofcode.com/2024/day/2/input", opts).body

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

Functions

valid_sequence? = fn sequence ->
  pairs = Enum.chunk_every(sequence, 2, 1, :discard)

  desc? =
    Enum.all?(pairs, fn [a, b] ->
      b > a and abs(a-b) <= 3
    end)

  asc? =
    Enum.all?(pairs, fn [a, b] ->
      a > b and abs(a-b) <= 3
    end)

  desc? or asc?
end

Puzzle 1

puzzle_1 = fn ->
  Enum.count(reports, &valid_sequence?.(&1))
end

puzzle_1.()

Puzzle 2

puzzle_2 = fn ->
  Enum.count(reports, fn report ->
    valid_with_deletion? = 
      Enum.with_index(report)
      |> Enum.map(fn {_el, i} ->
        List.delete_at(report, i) |> valid_sequence?.()
      end)
      |> Enum.any?()
  
    valid_with_deletion? or valid_sequence?.(report)
  end)
end

puzzle_2.()

Benchmarks

Benchee.run(
  %{
    "puzzle_1" => fn -> puzzle_1.() end,
    "puzzle_2" => fn -> puzzle_2.() end
  })