Advent Of Code

768 readers

1 users here now

An unofficial home for the advent of code community on programming.dev!

Advent of Code is an annual Advent calendar of small programming puzzles for a variety of skill sets and skill levels that can be solved in any programming language you like.

AoC 2023

Solution Threads

M	T	W	T	F	S	S
				1	2	3
4	5	6	7	8	9	10
11	12	13	14	15	16	17
18	19	20	21	22	23	24
25

Rules/Guidelines

Follow the programming.dev instance rules
Keep all content related to advent of code in some way
If what youre posting relates to a day, put in brackets the year and then day number in front of the post title (e.g. [2023 Day 10])
When an event is running, keep solutions in the solution megathread to avoid the community getting spammed with posts

Relevant Communities

Relevant Links

Advent of Code Homepage

Credits

Icon base by Lorc under CC BY 3.0 with modifications to add a gradient

console.log('Hello World')

founded 1 year ago

MODERATORS

[email protected]

🎁 - 2023 DAY 5 SOLUTIONS -🎁 (programming.dev)

submitted 11 months ago* (last edited 11 months ago) by [email protected] to c/[email protected]

39 comments fedilink hide all child comments

Day 5: If You Give a Seed a Fertilizer

Megathread guidelines

Keep top level comments as only solutions, if you want to say something other than a solution put it in a new post. (replies to comments can be whatever)
Code block support is not fully rolled out yet but likely will be in the middle of the event. Try to share solutions as both code blocks and using something such as https://topaz.github.io/paste/ , pastebin, or github (code blocks to future proof it for when 0.19 comes out and since code blocks currently function in some apps and some instances as well if they are running a 0.19 beta)

FAQ

What is this?: Here is a post with a large amount of details: https://programming.dev/post/6637268
Where do I participate?: https://adventofcode.com/
Is there a leaderboard for the community?: We have a programming.dev leaderboard with the info on how to join in this post: https://programming.dev/post/6631465

🔒This post will be unlocked when there is a decent amount of submissions on the leaderboard to avoid cheating for top spots

🔓 Unlocked after 27 mins (current record for time, hard one today)

you are viewing a single comment's thread
view the rest of the comments

[–] [email protected] 1 points 11 months ago* (last edited 11 months ago) (1 children)

I'm a little confused about this one. The mappings are total, that is any number that is not defined explicitly gets mapped to itself. So it's easy to create an example where the lowest number does not get mentioned within a range:

seeds: 0 3

seed-to-soil map:
10 0 2

soil-to-fertilizer map:
100 200 5

fertilizer-to-water map:
100 200 5

water-to-light map:
100 200 5

light-to-temperature map:
100 200 5

temperature-to-humidity map:
100 200 5

humidity-to-location map:
100 200 5

Here, we have seeds 0, 1 and 2. seed 0 gets mapped to location 10, seed 1 gets mapped to location 11 and seed 2 gets mapped to location 2. That means location 2 would be the answer, but it's not a start of any range. I guess this just doesn't happen in any of the inputs?

EDIT: actually it's double weird. If you implemented a backwards search, that is you create reverse mappings and then try out all locations (which is what I and many others did), the result of the above example is location 0, whereas if you create a forwards brute force of all seeds, the result is 2. For the reverse approach to work in all cases, the mappings would have to be bijective.

[–] [email protected] 1 points 11 months ago

Indeed, my solution fails on this input (returns 10, which is the location to seed 0), but it can be easily solved by also adding the ends of each range as well.

Maybe the input was quite forgiving. Thinking about it more, reversing the mapping can get quite involved, because it is neither surjective nor injective, so the inverse can actually have any number of results.

In your example there is no input that maps to 0, but there are two inputs that map to 11 (1 and 11). If the seed-to-soil map also included 10 20 2, 21 would also map to 11.