advent_of_code/elixir/livebook/2024/day13.livemd

AOC 2024 Day 13

Mix.install([
  {:nx, "0.9.2"}
])

Section

input = """
"""

for {a, b} <- (for line <- (input |> String.trim() |> String.split("\n")), reduce: {[], []} do
  {vecs, matrices} = acc -> 
   case line do
     "Button " <> rest ->
       [[_, a, b]] = Regex.scan(~r/[AB]: X\+(\d+), Y\+(\d+)/, rest)
       v = [a, b] |> Enum.map(&String.to_integer(&1))
       {[v | vecs], matrices}
     "Prize: " <> rest ->
       [[_, a, b]] = Regex.scan(~r/X=(\d+), Y=(\d+)/, rest)
       v = [a, b] |> Enum.map(&String.to_integer(&1))
       a = Nx.tensor(vecs, type: :f64) |> Nx.transpose()
       b = Nx.tensor(v |> Enum.map(&(&1+10000000000000)), type: :f64)
       {[], [{a, b} | matrices]}
     _ -> acc
   end
    end |> elem(1)),
    c = Nx.LinAlg.invert(a) |> Nx.dot(b)  |> Nx.round(),
    b_prime = Nx.dot(
        a, c
    ) |> Nx.round() |> Nx.as_type(:f64),
  c = Nx.as_type(c, :s64),
    b == b_prime,
  reduce: Nx.tensor(0, type: :s64)
  do
    acc2 ->
      c |> Nx.dot(Nx.tensor([1, 3], type: :s64)) |> Nx.add(acc2)
  end