Thanks! If I had known about Stream.drop/1, my part2_with_stream_iteration function would have looked like @sasajuric 's solution.
patrickcarver
2
factoryd
My solution is eerily similar to a lot of the posts here:
https://github.com/trbngr/advent_of_code/blob/master/lib/advent_of_code/2019/day1.ex
I did go back and replace the tests with doctests. Should help keep things clear going forward. Great idea!
2
debajit
My solutions for Day 1
- Part 1: advent-of-code-2019/day_01_rocket_equation/lib/part1.ex at master · debajit/advent-of-code-2019 · GitHub
- Part 2: advent-of-code-2019/day_01_rocket_equation/lib/part2.ex at master · debajit/advent-of-code-2019 · GitHub
I wrote them in a way that I thought was easy for me to reason about. I haven’t seen the answers above yet (I’m going to do that later tonight — I always learn so much new that way 
). Snippets below:
Part 1
defmodule Part1 do
@doc """
iex> fuel_for_mass(12)
2
iex> fuel_for_mass(14)
2
iex> fuel_for_mass(1969)
654
iex> fuel_for_mass(100756)
33583
"""
def fuel_for_mass(mass) do
div(mass, 3) - 2
end
def total_fuel(input_file) do
File.stream!(input_file)
|> Stream.map(&String.trim/1)
|> Stream.map(&String.to_integer/1)
|> Stream.map(&fuel_for_mass/1)
|> Enum.sum()
end
end
Part 2
defmodule Part2 do
@doc """
iex> fuel_for_mass(12)
2
iex> fuel_for_mass(14)
2
iex> fuel_for_mass(1969)
654
iex> fuel_for_mass(100756)
33583
"""
def fuel_for_mass(mass) do
div(mass, 3) - 2
end
@doc """
iex(9)> total_fuel_for_mass(14)
2
iex(10)> total_fuel_for_mass(1969)
966
iex(11)> total_fuel_for_mass(100756)
50346
"""
def total_fuel_for_mass(mass_or_fuel) do
fuel = fuel_for_mass(mass_or_fuel)
if fuel > 0 do
fuel + total_fuel_for_mass(fuel)
else
0
end
end
def total_fuel(input_file) do
File.stream!(input_file)
|> Stream.map(&String.trim/1)
|> Stream.map(&String.to_integer/1)
|> Stream.map(&total_fuel_for_mass/1)
|> Enum.sum()
end
end
1
qhwa
I’m learning Elixir with doing AOC and got improved a lot. Thanks to this post, I borrowed a lot of brilliant ideas from @sasajuric @dimitarvp and improved my repo. 
Here’s the day1 solution I end up with:
defmodule AOC.Y2019.Day01 do
@masses "2019/day01.txt"
|> AOC.Input.stream(&String.to_integer/1)
|> Enum.to_list()
def part1 do
@masses
|> Enum.reduce(0, &(div(&1, 3) - 2 + &2))
end
def part2 do
@masses
|> Enum.reduce(0, &(fuel(&1) + &2))
end
def fuel(mass) do
case div(mass, 3) - 2 do
x when x > 0 ->
x + fuel(x)
_ ->
0
end
end
end
2
ganesh
Here is mine
defmodule AOC.Day1 do
def part1(file_stream) do
file_stream
|> Enum.reduce(0, fn n, acc -> acc + calculate_fuel(n) end)
end
def part2(file_stream) do
file_stream
|> Enum.reduce(0, fn n, acc -> acc + additional_fuel(n, 0) end)
end
defp calculate_fuel(n), do: div(n, 3) - 2
defp additional_fuel(fuel, additional) when fuel < 6, do: additional
defp additional_fuel(fuel, additional) do
new_fuel = calculate_fuel(fuel)
additional_fuel(new_fuel, additional + new_fuel)
end
end
And here is test. I create file stream in the test
defmodule Day1Test do
use ExUnit.Case
alias AOC.Day1
test "solution day 1 part 1" do
input = read_input("test/input/day1_input")
assert Day1.part1(input) == 3_152_919
end
test "solution day 1 part 2" do
input = read_input("test/input/day1_input")
assert Day1.part2(input) == 4_726_527
end
defp read_input(file) do
file
|> File.stream!([], :line)
|> Stream.map(fn line ->
{integer, _leftover} = Integer.parse(line)
integer
end)
end
end
Repo: https://github.com/gsarwate/advent_of_code_2019/blob/master/lib/aoc/day1.ex
2
darkmarmot
and incorporating great suggestions in this thread, my “final” day 1 looks like:
defmodule AOC.Day1 do
def part1 do
AOC.integer_stream(1)
|> Enum.reduce(0, fn mass, acc -> fuel(mass) + acc end)
end
def part2 do
AOC.integer_stream(1)
|> Stream.map(&fuel/1)
|> Enum.reduce(0, fn mass, acc -> add_fuel(mass) + acc end)
end
def fuel(mass) do
max(0, trunc(mass / 3) - 2)
end
def add_fuel(mass) do
case fuel(mass) do
0 -> 0
f -> mass + add_fuel(f)
end
end
end
1
sb8244
Author of Real-Time Phoenix
AlchemistCamp
AlchemistCamp
That’s a great idea. Does the site let you start late or do you have to keep up every day?
0
