diff --git a/2024/day2.exs b/2024/day2.exs new file mode 100755 index 0000000..26e9277 --- /dev/null +++ b/2024/day2.exs @@ -0,0 +1,72 @@ +#!/usr/bin/env elixir +defmodule Day2 do + def part1(reports) do + Enum.count(reports, &check_report/1) + end + + def check_report([a, b | _]) when abs(b - a) not in [1, 2, 3], do: false + def check_report([a, b | rest]), do: check_report([b | rest], b - a) + def check_report([_], _dir), do: true + + def check_report([a, b | rest], dir) do + new_dir = b - a + + if ((dir < 0 and new_dir < 0) or (dir > 0 and new_dir > 0)) and abs(new_dir) <= 3 do + check_report([b | rest], new_dir) + else + false + end + end + + def part2(reports) do + Enum.count(reports, fn report -> + Enum.find_value(0..(length(report) - 1), false, fn dampen -> + {_, dampened} = List.pop_at(report, dampen) + check_report(dampened) + end) + end) + end + + def input do + with [input_filename] <- System.argv(), + {:ok, input} <- File.read(input_filename) do + input + |> String.split("\n", trim: true) + |> Enum.map(fn line -> line |> String.split() |> Enum.map(&String.to_integer/1) end) + 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 day2.exs input_filename") + end +end + +Day2.run()