2022 Day 5

2022/README.md

@@ -2,7 +2,7 @@
 
 My (attempted) solutions to [Advent of Code 2022](https://adventofcode.com/2022) in Elixir.
 
-<img width="855" alt="image" src="https://user-images.githubusercontent.com/498229/205479525-61bb1a75-3b77-4bff-a745-a27e29c3032e.png">
+<img width="866" alt="image" src="https://user-images.githubusercontent.com/498229/205664589-fc3a7666-b13e-41d2-87db-9b282e1ba8b8.png">
 
 ## Running:
 

2022/day5.exs

@@ -0,0 +1,90 @@
+defmodule Day5 do
+  def part1(input), do: input |> move_with(&move_9000/3) |> top_crates()
+  def part2(input), do: input |> move_with(&move_9001/3) |> top_crates()
+
+  defp move_with({stacks, procedure}, move) do
+    for [number, from_index, to_index] <- procedure, reduce: stacks do
+      stacks ->
+        {moved_from, moved_to} = move.(number, stacks[from_index], stacks[to_index])
+        %{stacks | from_index => moved_from, to_index => moved_to}
+    end
+  end
+
+  defp move_9000(0, from, to), do: {from, to}
+  defp move_9000(number, [crate | from], to), do: move_9000(number - 1, from, [crate | to])
+
+  defp move_9001(number, from, to) do
+    {moving, moved_from} = Enum.split(from, number)
+    {moved_from, moving ++ to}
+  end
+
+  defp top_crates(stacks) do
+    Enum.reduce(stacks, "", fn {_label, [top | _stack]}, acc -> acc <> top end)
+  end
+
+  def input do
+    with [input_filename] <- System.argv(),
+         {:ok, input} <- File.read(input_filename) do
+      [raw_stacks, raw_procedure] = String.split(input, "\n\n")
+
+      stacks =
+        raw_stacks
+        |> String.split("\n")
+        |> parse_stacks()
+        |> Enum.zip()
+        |> Enum.map(fn stack -> stack |> Tuple.to_list() |> Enum.drop_while(&is_nil/1) end)
+        |> Enum.with_index()
+        |> Map.new(fn {stack, index} -> {index + 1, stack} end)
+
+      procedure =
+        raw_procedure
+        |> String.split(["\n", " ", "move", "from", "to"], trim: true)
+        |> Enum.map(&String.to_integer/1)
+        |> Enum.chunk_every(3)
+
+      {stacks, procedure}
+    else
+      _ -> :error
+    end
+  end
+
+  defp parse_stacks([_labels_]), do: []
+  defp parse_stacks([line | rest]), do: [parse_line(line) | parse_stacks(rest)]
+
+  defp parse_line(<<"">>), do: []
+  defp parse_line(<<"    ", rest::binary>>), do: [nil | parse_line(rest)]
+  defp parse_line(<<"[", crate::binary-1, "]", rest::binary>>), do: [crate | parse_line(rest)]
+  defp parse_line(<<" ", rest::binary>>), do: parse_line(rest)
+
+  #######################
+  # 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("#{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 day5.exs input_filename")
+  end
+end
+
+Day5.run()