#!/usr/bin/env elixir defmodule Day3 do def part1(input) do Regex.scan(~r/mul\((\d+),(\d+)\)/, input, capture: :all_but_first) |> Enum.map(fn [a, b] -> String.to_integer(a) * String.to_integer(b) end) |> Enum.sum() end def part2(input) do Regex.scan(~r/mul\((\d+),(\d+)\)|do\(\)|don't\(\)/, input) |> Enum.reduce({0, :process}, fn ["do()"], {sum, _} -> {sum, :process} ["don't()"], {sum, _} -> {sum, :skip} _, {sum, :skip} -> {sum, :skip} [_, a, b], {sum, :process} -> {sum + String.to_integer(a) * String.to_integer(b), :process} end) |> elem(0) end def input do with [input_filename] <- System.argv(), {:ok, input} <- File.read(input_filename) do input else _ -> :error end end ####################### # HERE BE BOILERPLATE # ####################### def run do case input() do :error -> print_usage() input -> run_parts_with_timer(input) end end defp run_parts_with_timer(input) do run_with_timer(1, fn -> part1(input) end) run_with_timer(2, fn -> part2(input) end) end defp run_with_timer(part, fun) do {time, result} = :timer.tc(fun) IO.puts("Part #{part} (completed in #{format_time(time)}):\n") IO.puts("#{inspect(result)}\n") end defp format_time(μsec) when μsec < 1_000, do: "#{μsec}μs" defp format_time(μsec) when μsec < 1_000_000, do: "#{μsec / 1000}ms" defp format_time(μsec), do: "#{μsec / 1_000_000}s" defp print_usage do IO.puts("Usage: elixir day3.exs input_filename") end end Day3.run()