2023 Day 2

2023/day2.exs

@@ -0,0 +1,79 @@
+#!/usr/bin/env elixir
+defmodule Day2 do
+  def part1(input) do
+    input
+    |> Map.filter(fn {_id, cubes} ->
+      cubes["red"] <= 12 and cubes["green"] <= 13 and cubes["blue"] <= 14
+    end)
+    |> Map.keys()
+    |> Enum.sum()
+  end
+
+  def part2(input) do
+    input
+    |> Enum.map(fn {_id, cubes} -> cubes |> Map.values() |> Enum.product() end)
+    |> Enum.sum()
+  end
+
+  def input do
+    with [input_filename] <- System.argv(),
+         {:ok, input} <- File.read(input_filename) do
+      input
+      |> String.split("\n", trim: true)
+      |> Map.new(fn line ->
+        ["Game " <> id | rounds] = String.split(line, [": ", "; "])
+
+        rounds =
+          rounds
+          |> Enum.map(&parse_round/1)
+          |> Enum.reduce(
+            %{"red" => 0, "green" => 0, "blue" => 0},
+            &Map.merge(&1, &2, fn _colour, count1, count2 -> max(count1, count2) end)
+          )
+
+        {String.to_integer(id), rounds}
+      end)
+    else
+      _ -> :error
+    end
+  end
+
+  def parse_round(round) do
+    round
+    |> String.split([", ", " "])
+    |> Enum.chunk_every(2)
+    |> Map.new(fn [number, colour] -> {colour, String.to_integer(number)} 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()

dayN.exs

@@ -1,3 +1,4 @@
+#!/usr/bin/env elixir
 defmodule DayREPLACE_ME do
   def part1(input) do
     input
@@ -35,7 +36,7 @@ defmodule DayREPLACE_ME do
   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")
+    IO.puts("#{inspect result}\n")
   end
 
   defp format_time(μsec) when μsec < 1_000, do: "#{μsec}μs"