diff --git a/2024/day15.exs b/2024/day15.exs new file mode 100755 index 0000000..e639cb4 --- /dev/null +++ b/2024/day15.exs @@ -0,0 +1,118 @@ +#!/usr/bin/env elixir +defmodule Day15 do + def part1({warehouse, robot, moves}) do + attempt_moves(moves, robot, warehouse) + |> Enum.map(fn + {{x, y}, :box} -> x + y * 100 + _ -> 0 + end) + |> Enum.sum() + end + + def attempt_moves([], _robot, warehouse), do: warehouse + + def attempt_moves([move | next_moves], robot, warehouse) do + next = move.(robot) + + case Map.fetch(warehouse, next) do + :error -> + attempt_moves(next_moves, next, warehouse) + + {:ok, :wall} -> + attempt_moves(next_moves, robot, warehouse) + + {:ok, :box} -> + case get_pushable_boxes(next, move, warehouse, [next]) do + :wall -> + attempt_moves(next_moves, robot, warehouse) + + boxes -> + warehouse = + Enum.reduce(boxes, warehouse, fn box, warehouse -> + warehouse |> Map.delete(box) |> Map.put(move.(box), :box) + end) + + attempt_moves(next_moves, next, warehouse) + end + end + end + + def get_pushable_boxes(box, move, warehouse, pushable_boxes) do + next = move.(box) + + case Map.fetch(warehouse, next) do + :error -> pushable_boxes + {:ok, :wall} -> :wall + {:ok, :box} -> get_pushable_boxes(next, move, warehouse, [next | pushable_boxes]) + end + end + + def part2(_input) do + :boring_skipped + end + + def input do + with [input_filename] <- System.argv(), + {:ok, input} <- File.read(input_filename) do + [raw_map, raw_moves] = String.split(input, "\n\n") + + {_, _y, robot, map} = + for < "\n">>, reduce: {0, 0, nil, %{}} do + {x, y, robot, map} -> + case char do + "." -> {x + 1, y, robot, map} + "#" -> {x + 1, y, robot, Map.put(map, {x, y}, :wall)} + "O" -> {x + 1, y, robot, Map.put(map, {x, y}, :box)} + "@" -> {x + 1, y, {x, y}, map} + "\n" -> {0, y + 1, robot, map} + end + end + + moves = + for <> do + case char do + "^" -> fn {x, y} -> {x, y - 1} end + "v" -> fn {x, y} -> {x, y + 1} end + "<" -> fn {x, y} -> {x - 1, y} end + ">" -> fn {x, y} -> {x + 1, y} end + end + end + + {map, robot, moves} + 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 day15.exs input_filename") + end +end + +Day15.run()