AOC2020/aoc2020/lib/aoc20201210.dart

import 'dart:math';
import 'package:aoc2020/aocbase.dart';
import 'package:aoc2020/model/readdata.dart';

class AOC20201210 extends AOCBase {
  var mylist = <num>[];
  var dest = <num>[];

  void init(bool test) async {
    mylist = await ReadData.readFile<num>(classString, test: test);
    mylist.sort();
    mylist.insert(0, 0);
    mylist.add(mylist.last + 3);
    dest = [];
    for (var index = 1; index < mylist.length; index++) {
      dest.add(mylist[index] - mylist[index - 1]);
    }
  }

  @override
  Future<void> a({bool test}) async {
    await init(test);

    var hist = <num, num>{};
    for (var num in dest) {
      hist[num] = hist[num] == null ? 1 : hist[num] + 1;
    }
    // print(hist);
    answerA = hist[1] * hist[3];
  }

  @override
  Future<void> b({bool test}) async {
    var groups = <int, int>{};

    await init(test);

    // Count groups
    var groupStart = false;
    var groupCount = 0;
    for (var index = 0; index < dest.length; index++) {
      if (!groupStart && dest[index] == 1) {
        groupStart = true;
        groupCount = 0;
      }
      if (groupStart) {
        if (dest[index] != 1) {
          groupStart = false;
          groups[groupCount] = groups[groupCount] == null ? 1 : groups[groupCount] + 1;
        } else {
          groupCount++;
        }
      }
    }
    var multiplier = <num>[1, 2, 4];
    for (var index = 3; index < 30; index++) {
      multiplier.add(multiplier[index-1] + multiplier[index-2] + multiplier[index-3]);
    }
    // print(groups);
    answerB = 1;
    for (var group in groups.keys) {
      if (group > 1) {
        // print('for group $group ${multiplier[group]} ^ ${groups[group]}');
        answerB = answerB * pow(multiplier[group-1], groups[group]);
      }
    }
  }
}