From 1e74b21dc58b1052666ae64b916de6694e3e0227 Mon Sep 17 00:00:00 2001
From: Adam Millerchip <adam@millerchip.net>
Date: Mon, 4 Dec 2023 18:00:25 +0900
Subject: [PATCH] Day 4 part 1

---
 2023/day4.exs | 68 +++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 68 insertions(+)
 create mode 100644 2023/day4.exs

diff --git a/2023/day4.exs b/2023/day4.exs
new file mode 100644
index 0000000..9b02eab
--- /dev/null
+++ b/2023/day4.exs
@@ -0,0 +1,68 @@
+defmodule Day4 do
+  def part1(input) do
+    input
+    |> Enum.map(fn {_id, winning, have} ->
+      case MapSet.intersection(winning, have) |> MapSet.size() do
+        0 -> 0
+        num_winners -> 2 ** (num_winners - 1)
+      end
+    end)
+    |> Enum.sum()
+  end
+
+  def part2(_input) do
+    :ok
+  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 ->
+        [card_id, winning, have] = String.split(line, [": ", " | "])
+        ["Card", id] = String.split(card_id, " ", trim: true)
+
+        [winning, have] =
+          for cards <- [winning, have],
+              do: cards |> String.split(" ", trim: true) |> MapSet.new(&String.to_integer/1)
+
+        {String.to_integer(id), winning, have}
+      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 day4.exs input_filename")
+  end
+end
+
+# Day4.run()