Advent of Code 2024 Day 13 Part 1

Mix.install([
  {:kino_aoc, "~> 0.1"}
])

Get Inputs

{:ok, puzzle_input} =
  KinoAOC.download_puzzle("2024", "13", System.fetch_env!("LB_SESSION"))

My answer

sample_input =
  """
  Button A: X+94, Y+34
  Button B: X+22, Y+67
  Prize: X=8400, Y=5400
  
  Button A: X+26, Y+66
  Button B: X+67, Y+21
  Prize: X=12748, Y=12176
  
  Button A: X+17, Y+86
  Button B: X+84, Y+37
  Prize: X=7870, Y=6450
  
  Button A: X+69, Y+23
  Button B: X+27, Y+71
  Prize: X=18641, Y=10279
  """
  |> String.trim()

parse_machines = fn input ->
  input
  |> String.split("\n\n")
  |> Enum.map(fn machine_rows ->
    Regex.named_captures(
      ~r/\+(?\d+).*\+(?\d+)\n.*\+(?\d+).*\+(?\d+)\n.*=(?\d+).*=(?\d+)/,
      machine_rows
    )
  end)
  |> Enum.map(fn %{"ax" => ax, "ay" => ay, "bx" => bx, "by" => by, "px" => px, "py" => py} ->
    %{
      a: %{x: String.to_integer(ax), y: String.to_integer(ay)},
      b: %{x: String.to_integer(bx), y: String.to_integer(by)},
      prize: %{x: String.to_integer(px), y: String.to_integer(py)}
    }
  end)
end

machines = parse_machines.(sample_input)

get_prize = fn %{a: %{x: ax, y: ay}, b: %{x: bx, y: by}, prize: %{x: px, y: py}} ->
  for num_a <- 0..100,
      num_b <- 0..100,
      num_a * ax + num_b * bx == px,
      num_a * ay + num_b * by == py do
    {num_a, num_b}
  end
end

get_cost = fn machines ->
  machines
  |> Enum.map(fn machine ->
    machine
    |> get_prize.()
    |> Enum.map(fn {num_a, num_b} ->
      num_a * 3 + num_b
    end)
    |> case do
      [] -> 0
      costs -> Enum.min(costs)
    end
  end)
  |> Enum.sum()
end

get_cost.(machines)

puzzle_input
|> parse_machines.()
|> get_cost.()