2022 Day 10

2022/README.md

@@ -2,7 +2,7 @@
 
 My (attempted) solutions to [Advent of Code 2022](https://adventofcode.com/2022) in Elixir.
 
-<img width="869" alt="image" src="https://user-images.githubusercontent.com/498229/206719215-8b2da4f5-80a1-425e-b567-b92b7a0ca167.png">
+<img width="869" alt="image" src="https://user-images.githubusercontent.com/498229/206862407-902d0162-93b1-46c6-8bf1-1e7ec7e7f819.png">
 
 ## Running:
 

2022/day10.exs

@@ -0,0 +1,109 @@
+defmodule Day10 do
+  defmodule Instr do
+    defstruct cmd: nil, cycles: 0, amt: nil
+  end
+
+  def part1(input) do
+    process(input, _cycle = 1, _x = 1, _sample_at = 20, _sig = 0)
+  end
+
+  defp process([], _cycle, _x, _sample_at, sig), do: sig
+
+  defp process(instrs, cycle, x, sample_at, sig) when cycle == sample_at do
+    process(instrs, cycle, x, sample_at + 40, sig + cycle * x)
+  end
+
+  defp process([%Instr{cycles: 0} | rest], cycle, x, sample_at, sig) do
+    process(rest, cycle + 1, x, sample_at, sig)
+  end
+
+  defp process([instr = %Instr{cycles: 1, cmd: :noop} | rest], cycle, x, sample_at, sig) do
+    process([%Instr{instr | cycles: 0} | rest], cycle, x, sample_at, sig)
+  end
+
+  defp process([instr = %Instr{cycles: 1, cmd: :addx, amt: amt} | rest], cycle, x, sample_at, sig) do
+    process([%Instr{instr | cycles: 0} | rest], cycle, x + amt, sample_at, sig)
+  end
+
+  defp process([instr = %Instr{cycles: cycles} | rest], cycle, x, sample_at, sig) do
+    process([%Instr{instr | cycles: cycles - 1} | rest], cycle + 1, x, sample_at, sig)
+  end
+
+  def part2(input) do
+    input
+    |> scan(_x = 1, _pixel = 0, _pixels = [[]])
+    |> Enum.map(&Enum.reverse/1)
+    |> Enum.reverse()
+    |> Enum.join("\n")
+  end
+
+  defp scan([], _x, _pixel, pixels), do: pixels
+
+  defp scan(instrs, x, _pixel = 40, pixels) do
+    scan(instrs, x, _pixel = 0, [[] | pixels])
+  end
+
+  defp scan([%Instr{cmd: :noop} | rest], x, pixel, [row | pixels]) do
+    scan(rest, x, pixel + 1, [draw_pixel(pixel, x, row) | pixels])
+  end
+
+  defp scan([%Instr{cycles: 1, cmd: :addx, amt: amt} | rest], x, pixel, [row | pixels]) do
+    scan(rest, x + amt, pixel + 1, [draw_pixel(pixel, x, row) | pixels])
+  end
+
+  defp scan([instr = %Instr{cycles: cycles} | rest], x, pixel, [row | pixels]) do
+    scan([%Instr{instr | cycles: cycles - 1} | rest], x, pixel + 1, [
+      draw_pixel(pixel, x, row) | pixels
+    ])
+  end
+
+  defp draw_pixel(pixel, x, row) when pixel in (x - 1)..(x + 1), do: ["#" | row]
+  defp draw_pixel(_pixel, _x, row), do: [" " | row]
+
+  def input do
+    with [input_filename] <- System.argv(),
+         {:ok, input} <- File.read(input_filename) do
+      input
+      |> String.trim()
+      |> String.split("\n")
+      |> Enum.map(fn
+        "noop" -> %Instr{cmd: :noop, cycles: 1}
+        "addx " <> x -> %Instr{cmd: :addx, cycles: 2, amt: String.to_integer(x)}
+      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("#{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 day10.exs input_filename")
+  end
+end
+
+Day10.run()