2022 Day 3

2022/day3.exs

@@ -0,0 +1,71 @@
+defmodule Day3 do
+  def part1(input) do
+    input
+    |> Enum.map(fn str ->
+      size = byte_size(str)
+
+      str
+      |> String.split("", trim: true)
+      |> Enum.split(div(size, 2))
+    end)
+    |> Enum.map(fn {a, b} -> hd(a -- a -- b) end)
+    |> Enum.map(&score/1)
+    |> Enum.sum()
+  end
+
+  defp score(<<lower::utf8>>) when lower in ?a..?z, do: lower - ?a + 1
+  defp score(<<upper::utf8>>) when upper in ?A..?Z, do: upper - ?A + 27
+
+  def part2(input) do
+    input
+    |> Enum.map(&String.split(&1, "", trim: true))
+    |> Enum.chunk_every(3)
+    |> Enum.map(fn [a, b, c] ->
+      d = a -- a -- b
+      hd(d -- d -- c)
+    end)
+    |> Enum.map(&score/1)
+    |> Enum.sum()
+  end
+
+  def input do
+    with [input_filename] <- System.argv(),
+         {:ok, input} <- File.read(input_filename) do
+      String.split(input, "\n", trim: true)
+    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("#{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 day3.exs input_filename")
+  end
+end
+
+Day3.run()