Advent of Code 2019 - Day 1

bjorng · December 1, 2019, 6:43am

Note: This topic is to talk about Day 1 of the Advent of Code 2019.

bjorng · December 1, 2019, 6:44am

I used Advent of Code last year to learn some Elixir. Since I haven’t used Elixir much this year, I am using AOC 2019 as an opportunity to refresh my Elixir skills.

Here is my solution for my solution for Day 1.

NobbZ · December 1, 2019, 9:26am

There is room for improvement, eg by using Enum instead of Stream, and probably even more by doing manual recursion, but as I’m in the area of 0.05ms for part 2, I’ll just leave it as is.

gitlab.com

NobbZ/aoc_ex/blob/master/lib/y2019/d1.ex

defmodule AocEx.Y2019.D1 do
  use AocEx.Boilerplate,
    transform: fn raw -> raw |> String.split() |> Enum.map(&String.to_integer(&1)) end

  def part1(input \\ processed()) do
    input
    |> Stream.map(&calc_fuel/1)
    |> Enum.sum()
  end

  def part2(input \\ processed()) do
    input
    |> Stream.map(fn m -> m |> calc_fuel() |> add_fuel() end)
    |> Enum.sum()
  end

  defp calc_fuel(mass), do: div(mass, 3) - 2

  defp add_fuel(mass), do: add_fuel(mass, mass)

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egze · December 1, 2019, 9:47am

That‘s a cool Boilerplate you got there. Gonna borrow it next time

lakret · December 1, 2019, 11:49am

I will try something new this year, will live stream solving the challenges on Twitch. Today the stream starts at 2pm CET (in 1 hour 15 mins), here’s my channel Will be using Elixir, and maybe Rust for some challenges.

Last year’s solutions are here.

P.S. First day solution is here. Forgot to switch on “save past broadcasts”, will not forget next time Next stream will be on Tuesday at 7pm CET.

sasajuric · December 1, 2019, 3:47pm

Here’s my take.

alvises · December 1, 2019, 4:25pm

Hey guys,

here’s mine github repo for this aoc2019: alvises/aoc2019

And day1.ex

github.com

alvises/aoc2019/blob/master/lib/aoc2019/day1.ex

defmodule Aoc2019.Day1 do
  @type mass :: integer

  @doc """
  Gets the `fuel` needed to launch the given module's `mass`.

    ## Examples
      iex> Aoc2019.Day1.fuel(12)
      2
      iex> Aoc2019.Day1.fuel(14)
      2
      iex> Aoc2019.Day1.fuel(1969)
      654
      iex> Aoc2019.Day1.fuel(100756)
      33583
  """
  @spec fuel(mass) :: integer
  def fuel(mass) do
    mass
    |> div(3)

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simon · December 1, 2019, 4:27pm

I’m possibly going to have to refactor my repository structure but in any event my solution is here.

The aoc package is going to hold common code such as functions to load data from files.

Each day will be its own application and, compared to most I imagine, verbose. I like adding tests and some documentation.

simon · December 1, 2019, 4:29pm

I am so pleased that Saša is doing this again this year. His code tends to be incredibly compact and contains some lovely approaches which I’d not have thought about. Today I’ll be learning more about streams from him.

keathley · December 1, 2019, 8:26pm

I did mine in iex and translated to code after the fact: https://github.com/keathley/advent_of_code_2019/blob/master/day1.exs.

patrickcarver · December 1, 2019, 8:38pm

My own stab at Day 1:

github.com

patrickcarver/advent-of-code-2019-elixir/blob/master/day01/lib/day01.ex

defmodule Day01 do
  def part1 do
    run(&fuel_required/1)
  end

  def part2 do
    run(&total_fuel_required/1)
  end

  def part2_with_stream_iterate do
    run(&iterate/1)
  end

  def run(function_name) do
    module_masses()
    |> Stream.map(function_name)
    |> Enum.sum
  end

  def total_fuel_required(mass, acc \\ 0) do

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sergio · December 1, 2019, 9:12pm

This year I’m going to do my best to take a stab at this, using Elixir of course! Here’s my Day 1 solutions. I’m aiming for idiomatic elixir, that’s not too code-golfy.

github.com

sergiotapia/advent-of-code-2019-elixir/blob/master/day1/app-1.exs

"input.txt"
|> File.read!()
|> String.split("\n")
|> Enum.map(fn line ->
  (line |> String.to_integer() |> Integer.floor_div(3)) - 2
end)
|> Enum.sum()
|> IO.inspect()

# Answer is: 3490763

github.com

sergiotapia/advent-of-code-2019-elixir/blob/master/day1/app-2.exs

defmodule Fuel do
  def fuelForMass(0), do: 0
  def fuelForMass(mass) when mass < 0, do: 0
  def fuelForMass(mass) do
    fuel = (mass |> String.to_integer() |> Integer.floor_div(3)) - 2
    if fuel <= 0, do: 0, else: fuel + fuelForMass(Integer.to_string(fuel))
  end
end

"input.txt"
|> File.read!()
|> String.split("\n")
|> Enum.map(fn mass -> Fuel.fuelForMass(mass) end)
|> Enum.sum
|> IO.inspect

# Answer is: 5233250

dimitarvp · December 1, 2019, 9:48pm

Finished my pretty naive implementation as well: https://github.com/dimitarvp/aoc2019.ex/blob/master/lib/day1.ex

I opted for:

Common module helpers, for now just File.stream!-ing standardised file names from the priv/ project directory. You know, convenience.
Have a fuel and total_fuel functions, the latter being the recursive one.
Introducing doctests that exactly match the examples given in the task description.

Again, pretty naive and straightforward. Comments welcome!

dimitarvp · December 1, 2019, 10:13pm

@sasajuric Almost like mine! I also opted for a helper module that streams the file that maps to the day in question.

@patrickcarver:

  def iterate(mass) do
    mass
    |> Stream.iterate(&fuel_required/1)
    |> Enum.take_while(& &1 > 0)
    |> tl() # remove the module mass which would be the first in the list
    |> Enum.sum()
  end

That’s really clever, I love it!

@NobbZ Really solid code.

JEG2 · December 1, 2019, 10:16pm

My solution.

dimitarvp · December 1, 2019, 10:29pm

Somebody in the HackerNews thread posted quite readable bash solution.

sasajuric · December 1, 2019, 10:54pm

Yeah, I have a few common helpers, but I try to keep this as small as I can. So mostly reading the file input, and a few frequently needed enum helpers.

agundy · December 1, 2019, 10:59pm

Doing the challenge in Elixir this year. My day one solution is a little ugly but gets the job done. https://github.com/agundy/advent_of_code/blob/master/2019/solutions/lib/day_1.ex

dimitarvp · December 1, 2019, 10:59pm

Nice. One of my top priorities are terseness and readability. But I can give up some terseness in exchange for code that’s quicker to parse for any random reading human, and it seems you are the same.

Brofist?

darkmarmot · December 1, 2019, 11:03pm

My solution was pretty vanilla.

github.com

DarkMarmot/aoc_2019_elixir/blob/master/lib/day1.ex

defmodule Day1 do

  def part1 do
    input_stream()
    |> Stream.map(&calc_fuel/1)
    |> Enum.sum()
  end

  def part2 do
    input_stream()
    |> Stream.map(&calc_deep_fuel/1)
    |> Enum.sum()
  end

  def input_stream() do
    "./data/day1.txt"
    |> File.stream!()
    |> Stream.map(fn text -> Integer.parse(text) |> elem(0) end)
  end

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If the boilerplate strategy above holds, I might have to sneak something like that in!