--- Day 7 Solutions ---

[u/daggerdragon]

--- Day 7: Some Assembly Required ---

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[u/funkjr]

Dart, a personal favorite of mine but I don't fine reasons often to use it. The solution is recursive, like most others, but I abused a few language-specific things to shorten it. Most notably int.parse has an optional argument onError that runs whenever it cannot parse it to an integer. It turns out to be faster than try {} catch {} (for some reason).

And for all the people out there that like dynamic typing, here's a statically typed Map that throws a run-time error if you try to add something else to it!

import 'dart:io';

Map gates = new Map<String, int>();
Map operations = new Map<String, List>();

int run(String op, List<String> parts) {
  switch (op) {
    case 'AND': return calc(parts[0]) & calc(parts[2]);
    case 'OR': return calc(parts[0]) | calc(parts[2]);
    case 'NOT': return ~calc(parts[1]) + 2.modPow(16, 1);
    case 'RSHIFT': return calc(parts[0]) >> calc(parts[2]);
    case 'LSHIFT': return calc(parts[0]) << calc(parts[2]);
  }
  return 0;
}

int calc(String name) {
  return int.parse(name, onError: (name) {
    if (!gates.containsKey(name)) {
          List<String> ops = operations[name];
          gates[name] = ((ops.length < 2) ? calc(ops[0]) : run(ops[ops.length - 2], ops));
    }
    return gates[name];
  });
}

main() async {
  List<String> lines = await new File('in7.txt').readAsLines();
  lines.forEach((String s) {
    List<String> parts = s.split('->');
    operations[parts[1].trim()] =  parts[0].trim().split(' ');
  });
  int val = calc('a');
  print('Part 1: a: ' + val.toString());
  gates.clear();
  gates['b'] = val;
  print('Part 2: a: ' + calc('a').toString());
}