Advent of Code - Day 3

NobbZ · December 3, 2018, 11:19am

Note by the Moderators: This topic is to talk about Day 3 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.

And day 3 is solved as well.

On my VM in the office both parts take about 1 to 1.25 seconds. Thats OK for me today. But the first iteration I used to get the actual solutions has some repitions in it, which I do not like.

I really have to iterate on those, and perhaps I’ll be even able to get them more efficient?

gitlab.com

NobbZ/aoc_ex/blob/master/lib/y2018/d3.ex

defmodule AocEx.Y2018.D3 do
  use AocEx.Boilerplate,
    transform: fn raw ->
      raw
      |> String.split("\n")
      |> Enum.map(&String.split/1)
      |> Enum.map(fn ["#" <> id, "@", coord, size] ->
        id = String.to_integer(id)

        coord =
          coord
          |> String.trim(":")
          |> String.split(",")
          |> Enum.map(&String.to_integer/1)
          |> List.to_tuple()

        size =
          size
          |> String.split("x")
          |> Enum.map(&String.to_integer/1)

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sorentwo · December 3, 2018, 10:28pm

Finding a timely solution for Day 03 took me a little bit. Originally I wanted to use a range to detect overlap, but that wasn’t available so I moved on to constructing sets and counting from there. That wasn’t ideal either, and in the end using a simple map to count tuples was quick enough.

simon · December 4, 2018, 1:29am

Day 3 was the most time consuming so far but also the most satisfying because I’m getting a bit more confident with Enum and I’m also picking up ideas from @josevalim’s daily Twitch streams.

My day 3 code is at https://github.com/simon-wolf/advent-of-code-2018/blob/master/lib/advent_of_code_2018/day_03.ex

My main concern with all of my code so far is that I need to break it into smaller chunks and/or add more comments because I’m not entirely sure that I’ll understand it all by the end of the challenges. Or maybe I will because I’ll be much more familiar with Elixir than I am right now.

yawaramin · December 4, 2018, 6:16am

I approached Day 3 as a set intersection problem, the only issue was finding a data structure to represent the claims that would be usable as set elements (i.e. comparable for uniqueness). I realized I could cleanly map each claim to a set of coordinates of the exact square inches of that claim; after that the solution fell into place as a series of set intersections and unions.

Here it is: https://github.com/yawaramin/advent_of_code_2018/blob/d65581aeb7b25f40d22a05c1435b1401b2505fef/lib/day3.ex

Btw, I thought I’d share this fun fact that Elixir is in the top ten (at 10th) languages being used for Advent of Code projects on GitHub: https://github.com/search?o=desc&q=advent+of+code&s=updated&type=Repositories

debajit · December 4, 2018, 8:38am

My solution for Day 3 Part 1:

I’m reasonably happy with how it turned out.

(I spent quite a bit of time trying to learn how to use the Tensor library (Tensor.Matrix provides matrix operations). I also looked at Matrex, but failed to install it.

In the end I used a simple sparse matrix representation using a map with {row, col} => 1 items to represent the matrix. Using the regex named captures was fun — it was something I learned the hard way from a personal project previously.)

(Haven’t been able to look at Part 2 yet — its late night already, will look at it tomorrow)

github.com

debajit/advent-of-code-2018/blob/master/day-03-part-1-slice.exs

defmodule Claim do
  defstruct [:id, :left, :top, :width, :height]

  @claim_regex ~r/^\#(?<id>\d+) @ (?<left>\d+),(?<top>\d+): (?<width>\d+)x(?<height>\d+)$/

  def from_string(claim_string) do
    %{"id" => id, "left" => left, "top" => top, "width" => width, "height" => height} =
      Regex.named_captures(@claim_regex, claim_string)

    %Claim{
      id: String.to_integer(id),
      left: String.to_integer(left),
      top: String.to_integer(top),
      width: String.to_integer(width),
      height: String.to_integer(height)
    }
  end
end

defmodule NoMatterHowYouSliceIt do

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