Advent of Code 2018: Day 1 Part 1

Advent of Code (AOC) 2018 has finally arrived. This is the first time I participate in AOC. Last year, when I first heard of AOC, I wanted to participate in it. But due to heavy workload from university, I just give up on doing it.

This year, it’s different, I had graduated and working remotely. Hence, this year, I can schedule some time to work on this event. I am going to use Elixir to solve the puzzles this year. The codes will be available to my GitHub repo.

If things go well, I might continue writing down my journey on solving the puzzles of AOC 2018.

Without further ado, let’s start discussing the puzzles of Day 1.

Part 1

Part 1 is straightforward. A list of frequencies will given, and we have to sum up the frequencies. For example, from the problem descriptions:

Here are other example situations:

    +1, +1, +1 results in  3
    +1, +1, -2 results in  0
    -1, -2, -3 results in -6

So, the question of part 1 is:

Starting with a frequency of zero, what is the resulting frequency after all of the changes in frequency have been applied?

Straight forward and easy right?

So here is the puzzle inputs:

-9
+7
+5
-13
+6
...
-23
-46
-27
-11
-75223

Solution:

case File.read("input.txt") do
  {:ok, content} ->
    content
    |> String.split()
    |> Enum.map(&String.to_integer/1)
    |> Enum.sum
    |> IO.inspect
  {:error, _} -> IO.puts "Error opening files"
end

1. First, we read in the input from input.txt using File.read/1
2. Next, we split the content by newline using String.split/1. Now, we have a list of string representing the frequency.
3. Then, we map through the list with Enum.map/2 and convert the string to integer using String.to_integer/1.
4. Lastly, we call Enum.sum/2 to sum frequencies, which loops through every element in the list and add it up.

Performance: It takes around 0.3 seconds to compute the answer.

$ time elixir part-1.ex

real	0m0.350s
user	0m0.321s
sys	0m0.155s

Day 1 Part 1, Done.

Read Part 2 here.