From 9dd9b8f2e2c3293a6b8ee5bc208066dbbee67c81 Mon Sep 17 00:00:00 2001
From: Adam Millerchip <adam@millerchip.net>
Date: Tue, 6 Dec 2022 20:29:19 +0900
Subject: [PATCH] 2022 Day 6

---
 2022/README.md |  2 +-
 2022/day6.exs  | 72 ++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 73 insertions(+), 1 deletion(-)
 create mode 100644 2022/day6.exs

diff --git a/2022/README.md b/2022/README.md
index e258ae8..84e88ec 100644
--- a/2022/README.md
+++ b/2022/README.md
@@ -2,7 +2,7 @@
 
 My (attempted) solutions to [Advent of Code 2022](https://adventofcode.com/2022) in Elixir.
 
-<img width="866" alt="image" src="https://user-images.githubusercontent.com/498229/205664589-fc3a7666-b13e-41d2-87db-9b282e1ba8b8.png">
+<img width="866" alt="image" src="https://user-images.githubusercontent.com/498229/205899972-a06ef1bb-a870-48f0-8266-3a04f8515ee2.png">
 
 ## Running:
 
diff --git a/2022/day6.exs b/2022/day6.exs
new file mode 100644
index 0000000..670aa24
--- /dev/null
+++ b/2022/day6.exs
@@ -0,0 +1,72 @@
+defmodule Day6 do
+  @packet_marker_size 4
+  @message_marker_size 14
+
+  def part1(input) do
+    find_packet_marker(input)
+  end
+
+  defguardp all_different(a, b, c, d)
+            when a != b and a != c and a != d and b != c and b != d and c != d
+
+  defp find_packet_marker(buffer, seen \\ @packet_marker_size)
+  defp find_packet_marker([a, b, c, d | _rest], seen) when all_different(a, b, c, d), do: seen
+  defp find_packet_marker([_skip | rest], seen), do: find_packet_marker(rest, seen + 1)
+
+  def part2(input) do
+    find_message_marker(input)
+  end
+
+  defp find_message_marker([_skip | rest] = buffer, seen \\ @message_marker_size) do
+    window = Enum.take(buffer, @message_marker_size)
+
+    if Enum.uniq(window) == window do
+      seen
+    else
+      find_message_marker(rest, seen + 1)
+    end
+  end
+
+  def input do
+    with [input_filename] <- System.argv(),
+         {:ok, input} <- File.read(input_filename) do
+      input
+      |> String.trim()
+      |> String.codepoints()
+    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 day6.exs input_filename")
+  end
+end
+
+Day6.run()