AOC2022 day21

main.dart

// AOC 2022, Day 21: Monkey Math
// Build a tree
// 1) And visit it.
// 2) And fix the answer.
// https://dartpad.dev/?id=95d1e587ec0cf63b4cfe987e8a582fbf

final ops = {
  '+': (num a, num b) => a + b,
  '-': (num a, num b) => a - b,
  '*': (num a, num b) => a * b,
  '/': (num a, num b) => a / b,
};

class Node {
  String name;
  num _value = 0;
  Node(this.name);

  bool get isval => true;
  // overridden in subclass, so
  // ignore: unnecessary_getters_setters
  num get value => _value;
  set value(num n) => _value = n;
}

class CalcNode extends Node {
  late Node left;
  late Node right;
  late num Function(num, num) op;
  CalcNode(super.name);

  @override
  bool get isval => false;
  @override
  num get value => op(left.value, right.value);
}

var nodes = <String, Node>{};

buildLines(List<String> lines) {
  for (var line in lines) {
    var words = line.split(' ');
    var name = words[0].replaceAll(':', '');
    if (words.length == 2) {
      nodes[name] = Node(name)..value = int.parse(words[1]);
    } else {
      nodes[name] = CalcNode(name)
        ..left = Node(words[1])
        ..op = ops[words[2]]!
        ..right = Node(words[3]);
    }
  }
  connectNodes();
}

connectNodes() {
  for (var n in nodes.values.where((e) => !e.isval)) {
    (n as CalcNode)
      ..left = nodes[n.left.name]!
      ..right = nodes[n.right.name]!;
  }
}

part1(List<String> lines) {
  buildLines(lines);
  return nodes['root']!.value;
}

part2(List<String> lines) {
  buildLines(lines);
  // Let the network calculate the answer for us :-)
  var root = nodes['root']! as CalcNode..op = ops['-']!;
  var humn = nodes['humn']!..value = 0;
  var v1 = root.value;
  humn.value = 10000000000; // just need to make it big enough...
  var v2 = root.value;
  return v1 * humn.value ~/ (v1 - v2);
}

var testdata = [
  "root: pppw + sjmn",
  "dbpl: 5",
  "cczh: sllz + lgvd",
  "zczc: 2",
  "ptdq: humn - dvpt",
  "dvpt: 3",
  "lfqf: 4",
  "humn: 5",
  "ljgn: 2",
  "sjmn: drzm * dbpl",
  "sllz: 4",
  "pppw: cczh / lfqf",
  "lgvd: ljgn * ptdq",
  "drzm: hmdt - zczc",
  "hmdt: 32"
];

void main(List<String> args) {
  var dt = DateTime.now();
  assert(part1(testdata) == 152);
  assert(part2(testdata) == 301);
  var rt = DateTime.now().difference(dt).inMilliseconds;
  print('tests succeeded in $rt ms');
}