Advent of Code 2019 - Day 24

bjorng · December 24, 2019, 4:02pm

Note: This topic is to talk about Day 24 of the Advent of Code 2019.

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bjorng · December 24, 2019, 4:12pm

A fun one and much easier parsing than the donut maze on Pluto. It still took me a while to find and fix all the bugs for the edge and corner cases (pun intended).

Here is my solution.

sb8244 · December 24, 2019, 5:16pm

I thought this was a pretty creative problem, and conceptually simple to grasp. A good one for the end.

For part 2 I was a bit lazy and just hard coded the interesting neighbors with pattern matching. It was a bit of a pain when I pasted without updating, and then had to figure out why it was giving me the wrong answers.

github.com

sb8244/advent-of-code-2019/blob/master/lib/24.ex

defmodule TwentyFourRecursive do
  def parse(input) do
    # make the board bigger than the 200 ticks needed
    full =
      for r <- 0..4, c <- 0..4, d <- -150..150 do
        {{{r, c}, d}, "."}
      end
      |> Enum.into(%{})

    TwentyFour.parse(input)
    |> Enum.map(fn {coord, s} ->
      {{coord, 0}, s}
    end)
    |> Enum.into(full)
  end

  def next(state) do
    Enum.reduce(state, %{}, fn
      {p = {{2, 2}, _}, _}, next ->
        Map.put(next, p, "?")

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sasajuric · December 25, 2019, 8:22pm

I really disliked this problem (well, part 2 of it), to the point that I decided not to deal with it yesterday. I found it quite finicky, and otherwise not really challenging. My solution is here. The only semi-interesting thing is the part where I resolve inner/outer adjacent tiles at compile time. I’m not particularly happy with the code in general, nor with the running time (it takes about 2 seconds for the second part), but I don’t feel like improving it.