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Advent of Code 2024 Day 1 (adventofcode.com)

submitted 8 months ago* (last edited 7 months ago) by zongor@hexbear.net to c/programming@hexbear.net

9 comments fedilink hide all child comments

Alright so im going to force myself to create a post for this daily and maybe this will help force me to actually learn Elixir this year.

Please use Spoiler tags for your code snippets if they reveal answers.

Day 1 was interesting. Elixir is different, but it kinda reminds me of doing functional JavaScript but is wayyyyy nicer. It has so many tools to do stuff and the pattern matching is very powerful.

If anyone else wants me to tag them I can do that but I think @Enjoyer_of_Games@hexbear.net was the only one.

Heres my solution for Part 1:

spoiler

"input"    
    |> File.read!()
    |> String.split("\n")
    |> Enum.map(&String.split/1)
    |> Enum.filter(fn list -> length(list) == 2 end)
    |> Enum.map(fn [a, b] -> {String.to_integer(a), String.to_integer(b)} end)
    |> Enum.unzip()
    |> Tuple.to_list()
    |> Enum.map(&Enum.sort/1)
    |> Enum.zip()
    |> Enum.map(fn {a, b} -> abs(a - b) end)
    |> Enum.sum()

~~Ill post Part 2 later if I get time.~~ I had time, heres part 2:

spoiler

"input"    
    |> File.read!()
    |> String.split("\n")
    |> Enum.map(&String.split/1)
    |> Enum.filter(fn list -> length(list) == 2 end)
    |> Enum.map(fn [a, b] -> {String.to_integer(a), String.to_integer(b)} end)
    |> Enum.unzip()
    |> Tuple.to_list()
    |> Enum.map(&Enum.sort/1)
    |> (fn [list1, list2] -> {list1, Enum.frequencies(list2)} end).()
    |> (fn {list1, freqs} ->
          list1
          |> Enum.map(&{&1, Map.get(freqs, &1, 0)})
          |> Enum.filter(fn {_, count} -> count != 0 end)
          |> Enum.map(fn {value, count} -> value * count end)
        end).()
    |> Enum.sum()

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[–] kota@hexbear.net 2 points 8 months ago

Guess I'm a bit late on day one. Wound up doing mine in go, but maybe if I'm motivated I'll use something cooler later. Those elixir solutions are rad!

part 1

func main() {
	b, err := os.ReadFile("input.txt")
	if err != nil {
		log.Fatalln(err)
	}

	d, err := distance(string(b))
	if err != nil {
		log.Fatalln(err)
	}
	fmt.Println(d)
}

func distance(input string) (int, error) {
	var left []int
	var right []int
	for _, line := range strings.Split(input, "\n") {
		fields := strings.Fields(line)
		if len(fields) != 2 {
			continue
		}

		l, err := strconv.Atoi(fields[0])
		if err != nil {
			return 0, err
		}
		left = append(left, l)

		r, err := strconv.Atoi(fields[1])
		if err != nil {
			return 0, err
		}
		right = append(right, r)
	}

	slices.Sort(left)
	slices.Sort(right)

	var total int
	for i := 0; i < len(left); i++ {
		total += int(math.Abs(float64(left[i] - right[i])))
	}

	return total, nil
}

part 2

func main() {
	b, err := os.ReadFile("input.txt")
	if err != nil {
		log.Fatalln(err)
	}

	s, err := similarity(string(b))
	if err != nil {
		log.Fatalln(err)
	}
	fmt.Println(s)
}

func similarity(input string) (int, error) {
	collisions := make(map[int]int)
	var left []int
	var right []int
	for _, line := range strings.Split(input, "\n") {
		fields := strings.Fields(line)
		if len(fields) != 2 {
			continue
		}

		l, err := strconv.Atoi(fields[0])
		if err != nil {
			return 0, err
		}
		left = append(left, l)
		collisions[l] = 0

		r, err := strconv.Atoi(fields[1])
		if err != nil {
			return 0, err
		}
		right = append(right, r)
	}

	for _, r := range right {
		c := collisions[r]
		collisions[r] = c + 1
	}

	var total int
	for _, l := range left {
		v := collisions[l]
		total += l * v
	}

	return total, nil
}