110 lines
3.1 KiB
Elixir
110 lines
3.1 KiB
Elixir
defmodule Day10 do
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defmodule Instr do
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defstruct cmd: nil, cycles: 0, amt: nil
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end
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def part1(input) do
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process(input, _cycle = 1, _x = 1, _sample_at = 20, _sig = 0)
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end
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defp process([], _cycle, _x, _sample_at, sig), do: sig
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defp process(instrs, cycle, x, sample_at, sig) when cycle == sample_at do
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process(instrs, cycle, x, sample_at + 40, sig + cycle * x)
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end
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defp process([%Instr{cycles: 0} | rest], cycle, x, sample_at, sig) do
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process(rest, cycle + 1, x, sample_at, sig)
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end
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defp process([instr = %Instr{cycles: 1, cmd: :noop} | rest], cycle, x, sample_at, sig) do
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process([%Instr{instr | cycles: 0} | rest], cycle, x, sample_at, sig)
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end
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defp process([instr = %Instr{cycles: 1, cmd: :addx, amt: amt} | rest], cycle, x, sample_at, sig) do
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process([%Instr{instr | cycles: 0} | rest], cycle, x + amt, sample_at, sig)
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end
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defp process([instr = %Instr{cycles: cycles} | rest], cycle, x, sample_at, sig) do
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process([%Instr{instr | cycles: cycles - 1} | rest], cycle + 1, x, sample_at, sig)
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end
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def part2(input) do
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input
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|> scan(_x = 1, _pixel = 0, _pixels = [[]])
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|> Enum.map(&Enum.reverse/1)
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|> Enum.reverse()
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|> Enum.join("\n")
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end
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defp scan([], _x, _pixel, pixels), do: pixels
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defp scan(instrs, x, _pixel = 40, pixels) do
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scan(instrs, x, _pixel = 0, [[] | pixels])
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end
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defp scan([%Instr{cmd: :noop} | rest], x, pixel, [row | pixels]) do
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scan(rest, x, pixel + 1, [draw_pixel(pixel, x, row) | pixels])
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end
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defp scan([%Instr{cycles: 1, cmd: :addx, amt: amt} | rest], x, pixel, [row | pixels]) do
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scan(rest, x + amt, pixel + 1, [draw_pixel(pixel, x, row) | pixels])
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end
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defp scan([instr = %Instr{cycles: cycles} | rest], x, pixel, [row | pixels]) do
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scan([%Instr{instr | cycles: cycles - 1} | rest], x, pixel + 1, [
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draw_pixel(pixel, x, row) | pixels
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])
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end
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defp draw_pixel(pixel, x, row) when pixel in (x - 1)..(x + 1), do: ["#" | row]
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defp draw_pixel(_pixel, _x, row), do: [" " | row]
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def input do
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with [input_filename] <- System.argv(),
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{:ok, input} <- File.read(input_filename) do
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input
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|> String.trim()
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|> String.split("\n")
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|> Enum.map(fn
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"noop" -> %Instr{cmd: :noop, cycles: 1}
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"addx " <> x -> %Instr{cmd: :addx, cycles: 2, amt: String.to_integer(x)}
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end)
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else
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_ -> :error
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end
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end
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#######################
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# HERE BE BOILERPLATE #
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#######################
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def run do
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case input() do
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:error -> print_usage()
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input -> run_parts_with_timer(input)
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end
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end
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defp run_parts_with_timer(input) do
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run_with_timer(1, fn -> part1(input) end)
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run_with_timer(2, fn -> part2(input) end)
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end
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defp run_with_timer(part, fun) do
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{time, result} = :timer.tc(fun)
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IO.puts("Part #{part} (completed in #{format_time(time)}):\n")
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IO.puts("#{result}\n")
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end
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defp format_time(μsec) when μsec < 1_000, do: "#{μsec}μs"
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defp format_time(μsec) when μsec < 1_000_000, do: "#{μsec / 1000}ms"
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defp format_time(μsec), do: "#{μsec / 1_000_000}s"
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defp print_usage do
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IO.puts("Usage: elixir day10.exs input_filename")
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end
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end
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Day10.run()
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