Day 13: Claw Contraption

Mix.install([:kino])

Section

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

input = Kino.Input.read(input)

Part 1 & 2

defmodule ClawContraption do
  def parse(input) do
    input
    |> String.split("\n", trim: true)
    |> Enum.chunk_every(3)
    |> Enum.map(fn [a, b, p] ->
      [ax, ay] =
        String.split(a, ["Button A: X+", ", Y+"], trim: true) |> Enum.map(&String.to_integer/1)

      [bx, by] =
        String.split(b, ["Button B: X+", ", Y+"], trim: true) |> Enum.map(&String.to_integer/1)

      [px, py] =
        String.split(p, ["Prize: X=", ", Y="], trim: true) |> Enum.map(&String.to_integer/1)

      {{ax, ay}, {bx, by}, {px, py}}
    end)
  end

  def solve_part1(input) do
    input
    |> parse()
    |> Enum.map(fn {{ax, ay}, {bx, by}, {px, py}} ->
      ca = div(by * px - bx * py, by * ax - bx * ay)
      cb = div(ay * px - ax * py, ay * bx - ax * by)

      if ca * ax + cb * bx == px && ca * ay + cb * by == py do
        3 * ca + cb
      else
        0
      end
    end)
    |> Enum.sum()
  end

  def solve_part2(input) do
    add = 10_000_000_000_000

    input
    |> parse()
    |> Enum.map(fn {{ax, ay}, {bx, by}, {px, py}} ->
      ca = div(by * (px + add) - bx * (py + add), by * ax - bx * ay)
      cb = div(ay * (px + add) - ax * (py + add), ay * bx - ax * by)

      if ca * ax + cb * bx == px + add && ca * ay + cb * by == py + add do
        3 * ca + cb
      else
        0
      end
    end)
    |> Enum.sum()
  end
end

ClawContraption.solve_part1(input)
ClawContraption.solve_part2(input)