From 748e0a231179618918ae352b8b75a7a7f056712b Mon Sep 17 00:00:00 2001
From: Adam Millerchip <adam@millerchip.net>
Date: Fri, 2 Dec 2022 19:59:40 +0900
Subject: [PATCH] 2022 day 2

---
 2022/README.md |   2 +-
 2022/day2.exs  | 100 +++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 101 insertions(+), 1 deletion(-)
 create mode 100644 2022/day2.exs

diff --git a/2022/README.md b/2022/README.md
index a861917..a50b346 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="857" alt="image" src="https://user-images.githubusercontent.com/498229/205085139-d7b591b9-0d20-42ea-a650-250e965721a0.png">
+<img width="854" alt="image" src="https://user-images.githubusercontent.com/498229/205277538-b1b77935-742f-44fb-82c3-19608530b118.png">
 
 ## Running:
 
diff --git a/2022/day2.exs b/2022/day2.exs
new file mode 100644
index 0000000..f598a29
--- /dev/null
+++ b/2022/day2.exs
@@ -0,0 +1,100 @@
+defmodule Day2 do
+  def part1(input) do
+    input
+    |> Enum.map(fn
+      {opponent, "X"} -> {opponent, :rock}
+      {opponent, "Y"} -> {opponent, :paper}
+      {opponent, "Z"} -> {opponent, :scissors}
+    end)
+    |> Enum.map(&play/1)
+    |> Enum.sum()
+  end
+
+  @rock 1
+  @paper 2
+  @scissors 3
+  @lose 0
+  @draw 3
+  @win 6
+
+  defp play({:rock, :rock}), do: @rock + @draw
+  defp play({:paper, :rock}), do: @rock + @lose
+  defp play({:scissors, :rock}), do: @rock + @win
+  defp play({:rock, :paper}), do: @paper + @win
+  defp play({:paper, :paper}), do: @paper + @draw
+  defp play({:scissors, :paper}), do: @paper + @lose
+  defp play({:rock, :scissors}), do: @scissors + @lose
+  defp play({:paper, :scissors}), do: @scissors + @win
+  defp play({:scissors, :scissors}), do: @scissors + @draw
+
+  def part2(input) do
+    input
+    |> Enum.map(fn
+      {opponent, "X"} -> {opponent, :lose}
+      {opponent, "Y"} -> {opponent, :draw}
+      {opponent, "Z"} -> {opponent, :win}
+    end)
+    |> Enum.map(&play2/1)
+    |> Enum.sum()
+  end
+
+  defp play2({:rock, :win}), do: @win + @paper
+  defp play2({:paper, :win}), do: @win + @scissors
+  defp play2({:scissors, :win}), do: @win + @rock
+  defp play2({:rock, :draw}), do: @draw + @rock
+  defp play2({:paper, :draw}), do: @draw + @paper
+  defp play2({:scissors, :draw}), do: @draw + @scissors
+  defp play2({:rock, :lose}), do: @lose + @scissors
+  defp play2({:paper, :lose}), do: @lose + @rock
+  defp play2({:scissors, :lose}), do: @lose + @paper
+
+  def input do
+    with [input_filename] <- System.argv(),
+         {:ok, input} <- File.read(input_filename) do
+      input
+      |> String.split([" ", "\n"], trim: true)
+      |> Enum.map(fn
+        "A" -> :rock
+        "B" -> :paper
+        "C" -> :scissors
+        me -> me
+      end)
+      |> Enum.chunk_every(2)
+      |> Enum.map(&List.to_tuple/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("#{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()