A modern programming language that makes developers happier.

kotlinlang

:christmas_tree: Day 23 : Solutions Thread

Untitled

Brute force using mutable lists will work for Part 1 but will never scale for Part 2.
Opted to use an array rather than implementing ListedList-style nodes, each array[n] points to the element following n in the sequence.  Moving a block is then simply a matter of changing three elements in the array.

<https://github.com/ephemient/aoc2020/blob/main/kt/src/main/kotlin/io/github/ephemient/aoc2020/Day23.kt> array go brrrr

it's all about the data structures your language of choice allows you to use... and when it does not provide one, you wrote that yourself. Lo and behold: Fully functional linked list node in Kotlin:
```class Cup(val id: Int) {
    lateinit var next: Cup
}```
:troll:

image.png

and whole solution (sans init block, collapsed for readability):

is it just me or is that class missing all the stuff that makes a linked list worth using

<@U9ETWUAUD> - I had the same idea as you, but my node class (also called `Cup`!) can do a `toString()` until it loops around and has a function to gather the next `n` cups into a list (which I use twice). Most everything else is in my `Cups` class, which looks a bit different. It takes ~5s on my machine to do P2, which I guess is fine.

Also - got 1.20s on surefire (JVM) and 1.36s on jsBrowserTest on github actions worker :slightly_smiling_face:

Wow that is quick. I'm probably not doing the "next 3" part as efficiently as you are.

&lt;300ms on JVM for me. thanks to primitive arrays and no abstraction

Blog: <https://todd.ginsberg.com/post/advent-of-code/2020/day23/>

Code: <https://github.com/tginsberg/advent-2020-kotlin/blob/main/src/main/kotlin/com/ginsberg/advent2020/Day23.kt>

Probably could make that faster if I didn't implement the next 3 the way I did, but meh.

I used the `operator fun componentX` to extract the few next ones without building intermediate lists, but I can't chain calls with that approach

Too lazy to do the -1'ing for a list so i just used a map :slightly_smiling_face:

generate sequence is extremely slick here

I have a solution that works for 10 but not 100…

I think I have a fast and super simple solution (lets see in part2)