From 79638bc9c967460d778343d60e899bce209f04a9 Mon Sep 17 00:00:00 2001
From: Adam Millerchip <adam@millerchip.net>
Date: Sun, 22 Dec 2024 18:34:59 +0900
Subject: [PATCH] 2024 Day 22 Part 1

---
 2024/day22.exs | 69 ++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 69 insertions(+)
 create mode 100755 2024/day22.exs

diff --git a/2024/day22.exs b/2024/day22.exs
new file mode 100755
index 0000000..811dd63
--- /dev/null
+++ b/2024/day22.exs
@@ -0,0 +1,69 @@
+#!/usr/bin/env elixir
+defmodule Day22 do
+  def part1(input) do
+    Enum.sum_by(input, fn secret ->
+      Enum.reduce(1..2000, secret, fn _, secret -> next(secret) end)
+    end)
+  end
+
+  def next(secret) do
+    secret
+    |> Kernel.*(64)
+    |> mix(secret)
+    |> prune()
+    |> then(fn secret -> div(secret, 32) |> mix(secret) end)
+    |> prune()
+    |> then(fn secret -> (secret * 2048) |> mix(secret) end)
+    |> prune()
+  end
+
+  def mix(num, secret), do: Bitwise.bxor(secret, num)
+  def prune(secret), do: rem(secret, 16_777_216)
+
+  def part2(_input) do
+    :not_implemented
+  end
+
+  def input do
+    with [input_filename] <- System.argv(),
+         {:ok, input} <- File.read(input_filename) do
+      input
+      |> String.split("\n", trim: true)
+      |> Enum.map(&String.to_integer/1)
+    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 day22.exs input_filename")
+  end
+end
+
+Day22.run()