Advent of Code 2019 - Day 12

bjorng

Erlang Core Team

Note: This topic is to talk about Day 12 of the Advent of Code 2019.

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15 comments

#2019 #advent-of-code

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2019-12-13 09:12:20 UTC

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bjorng

Erlang Core Team

Fun, but tricky!

Here is my solution.

Post #1

cblavier

Just starting to read the instructions, sound tricky indeed.
Is there a typo in applied velocity example? I believe new x should be 3

Post #2

bjorng

Erlang Core Team

No, it seems to be correct.

Adding 1 and -2 gives -1. Did you try to subtract -2 from 1?

Post #3

cblavier

Replying to myself: x velocity is -2 and not simply 2

It’s going to be tough

Post #4

QuinnWilton

Part 2 was tough, but I enjoyed it!

I thought I was being clever by walking forward and backward at the same time, but that still took too long.

Post #5

sasajuric

Author of Elixir In Action

This is my solution. Takes about 15sec for the second part. I’m not doing it very efficiently since I’m computing per-dimension cycle from scratch, so I have to do three large passes, when I could solve everything in one. I should probably also replace the stream-based logic with Enum.reduce_while or a recursion. But I was too lazy for that, and this produced the result within a “reasonable” time.

Post #6

aaronnamba

I couldn’t figure out part 2 on my own, the puzzle title made me read up on the N-Body Problem, which made me .

After a couple hours of spinning my wheels (and my computer’s fans), I went looking for the tiniest hint (not spoiler/solution) I could find, which I ended up getting from this post from reddit.

Once I got the basic idea, it took just a couple minutes to code up a solution. And that gave me an answer in about 1 second. Sheesh.

My eventual part 2 solution

Post #7

xfix

I didn’t figure out the trick myself. Oh well.

gitlab.com/KonradBorowski/advent_of_code_2019

lib/day12.ex

master

defmodule AdventOfCode2019.Day12 do
  @moduledoc """
  Day 12 solutions
  """

  @doc ~S"""
  Solves the first riddle of day 12.

  ## Examples

      iex> AdventOfCode2019.Day12.part1("<x=3, y=-6, z=6>\n<x=10, y=7, z=-9>\n<x=-3, y=-7, z=9>\n<x=-8, y=0, z=4>")
      6849

  """
  def part1(input) do
    1..1000
    |> Enum.reduce(parse_planets(input), fn _, planets -> Enum.map(planets, &run_step/1) end)
    |> Enum.map(fn arg -> Enum.map(arg, &Tuple.to_list/1) end)
    |> Enum.zip()
    |> Enum.map(&Tuple.to_list/1)

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Post #8

jenarvaezg

My solution for today, sadly I got spoiled for part2, but I don’t think I’d have come up with the solution by myself anyways

Post #9

ihabunek

Here is mine. Like many people here, I also required a hint for part 2, so feeling a little stupid. But after that had no problems and the program runs under 1 second.

Post #10

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