diff --git a/2024/day1.exs b/2024/day1.exs new file mode 100755 index 0000000..7602f74 --- /dev/null +++ b/2024/day1.exs @@ -0,0 +1,66 @@ +#!/usr/bin/env elixir +defmodule Day1 do + def part1({list1, list2}) do + list1 = Enum.sort(list1) + list2 = Enum.sort(list2) + + distances(list1, list2) |> Enum.sum() + end + + def distances([], []), do: [] + def distances([h1 | t1], [h2 | t2]), do: [abs(h1 - h2) | distances(t1, t2)] + + def part2({list1, list2}) do + frequencies = Enum.frequencies(list2) + Enum.reduce(list1, 0, fn item, count -> count + item * Map.get(frequencies, item, 0) end) + end + + def input do + with [input_filename] <- System.argv(), + {:ok, input} <- File.read(input_filename) do + integers = + input + |> String.split([" ", "\n"], trim: true) + |> Enum.map(&String.to_integer/1) + + list1 = Enum.take_every(integers, 2) + list2 = Enum.take_every(tl(integers), 2) + + {list1, list2} + 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 day1.exs input_filename") + end +end + +Day1.run()