Day 4: Scratchcards


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  • mykl@lemmy.world
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    11 months ago

    Dart Solution

    Okay, that’s more like it. Simple parsing and a bit of recursion, and fits on one screen. Perfect for day 4 :-)

    int matchCount(String line) => line
        .split(RegExp('[:|]'))
        .skip(1)
        .map((ee) => ee.trim().split(RegExp(r'\s+')).map(int.parse))
        .map((e) => e.toSet())
        .reduce((s, t) => s.intersection(t))
        .length;
    
    late List matches;
    late List totals;
    
    int scoreFor(int ix) {
      if (totals[ix] != 0) return totals[ix];
      return totals[ix] =
          [for (var m in 0.to(matches[ix])) scoreFor(m + ix + 1) + 1].sum;
    }
    
    part1(List lines) =>
        lines.map((e) => pow(2, matchCount(e) - 1).toInt()).sum;
    
    part2(List lines) {
      matches = [for (var e in lines) matchCount(e)];
      totals = List.filled(matches.length, 0);
      return matches.length + 0.to(matches.length).map(scoreFor).sum;
    }