Day 11: Plutonian Pebbles
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)
- You can send code in code blocks by using three backticks, the code, and then three backticks or use something such as https://topaz.github.io/paste/ if you prefer sending it through a URL
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
You are viewing a single thread.
View all comments 
2 points
*
Dart
I really wish Dart had memoising built in. Maybe the new macro feature will allow this to happen, but in the meantime, here’s my hand-rolled solution.
import 'package:collection/collection.dart';
var counter_ = <(int, int), int>{};
int counter(s, [r = 75]) => counter_.putIfAbsent((s, r), () => _counter(s, r));
int _counter(int stone, rounds) =>
(rounds == 0) ? 1 : next(stone).map((e) => counter(e, rounds - 1)).sum;
List<int> next(int s) {
var ss = s.toString(), sl = ss.length;
if (s == 0) return [1];
if (sl.isOdd) return [s * 2024];
return [ss.substring(0, sl ~/ 2), ss.substring(sl ~/ 2)]
.map(int.parse)
.toList();
}
solve(List<String> lines) => lines.first.split(' ').map(int.parse).map(counter).sum;
