Advent of Code - Day 17

sasajuric · December 17, 2018, 3:31pm

Note: This topic is to talk about Day 17 of the Advent of Code.

For general discussion about the Advent of Code 2018 and links to topics of the other days, see this topic.

sasajuric · December 17, 2018, 3:31pm

Today was quite tricky. In the end I solved it by using a depth-first recursive approach. It works reasonably fast (under a second). The code is available here.

bjorng · December 17, 2018, 7:45pm

Here is my solution. It runs in about 30 seconds.

JEG2 · December 19, 2018, 12:14am

Here’s my solution:

github.com

JEG2/advent_of_code_2018/blob/master/day_17/reservoir_research.exs

defmodule ReservoirResearch do
  defstruct meters: Map.new, depth: nil, flow: [fall: {500, 0}]

  def parse(lines) do
    state = %__MODULE__{ }
    new_meters = Enum.reduce(lines, state.meters, fn line, meters ->
      line
      |> parse_meters
      |> Enum.reduce(meters, fn xy, meters ->
        Map.put(meters, xy, :clay)
      end)
    end)
    {min_y, max_y} =
      new_meters |> Map.keys |> Enum.map(&elem(&1, 1)) |> Enum.min_max
    %__MODULE__{
      state |
      meters: new_meters,
      depth: max_y,
      flow: [fall: {500, min_y - 1}]
    }

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It’s very fast, but I admit that I had to download @sasajuric’s code to figure out how to fix a particularly nasty bug I introduced.