Day 4: Scratchcards

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  • @mykl
    3•1 year 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;
}