AOC2021 Day14

import 'dart:io';
import 'package:more/more.dart';
import 'package:collection/collection.dart';

late List<String> polymer;
late Map<String, String> inserts;
late Multiset<String> counts;

MapEntry<T, T> me<T>(List<T> l) => MapEntry<T, T>(l.first, l.last); //helper
parseLines(List<String> lines) {
  var ls = lines.splitBefore((e) => e.isEmpty).toList();
  polymer = ls.first.first.split('');
  counts = Multiset.from(polymer.window(2).map((e) => e.join()));
  inserts = Map.fromEntries(ls.last.skip(1).map((e) => me(e.split(' -> '))));
}

applyInserts() {
  var copy = Multiset.from(counts);
  for (var before in inserts.keys) {
    var after = inserts[before];
    if (after != null) {
      var c = counts[before];
      copy[before] -= c;
      copy[before[0] + after] += c;
      copy[after + before[1]] += c;
    }
  }
  // Could use this to allow almost infinite growth, but two letter pairs
  // only ever appear once each (SO, OK).
  // if (copy.isNotEmpty) {
  //   var mn = copy.counts.min() - 1;
  //   for (var k in copy.distinct.toList()) {
  //     copy[k] -= mn;
  //   }
  // }
  counts = copy;
}

score() {
  var sums = Multiset<String>();
  for (var k in counts.distinct) {
    sums[k[0]] += counts[k];
  }
  sums[polymer.last] += 1; // OBOE
  var occs = sums.counts.sorted((a, b) => b.compareTo(a));
  return occs.first - occs.last;
}

main() {
  var lines = File('data/data14_01.txt').readAsLinesSync();
  var t = DateTime.now();
  parseLines(lines);
  0.to(10).forEach((e) => applyInserts());
  print(score()); //3408
  parseLines(lines);
  0.to(40).forEach((e) => applyInserts());
  print(score()); // 3724343376942

  print('${DateTime.now().difference(t).inMilliseconds} milliseconds');
}