AOC2021 Day24

///INTERPRET SOME MACHINE CODE.
// We want to build a pool of states, and understand which lead where.
// Once we have these, we want to find the most (then least) *expensive* route where
// at each step cost = (10* cost sofar) + next digit. (ie number made by
// joining all digits so far).

import 'dart:io';

import 'package:more/more.dart';
import 'package:collection/collection.dart';

late List<List<int>> params;
buildParams(List<String> lines) {
  var sections = lines.splitBefore((e) => e.startsWith('inp'));
  params = sections
      .map((s) => [
            for (var i in [4, 5, 15]) int.parse(s[i].split(' ')[2])
          ])
      .toList();
}

int buildNodes([bool mn = false]) {
  // `z` is the only part of state that actually gets used.
  // build a map of current `z`s and their best(highest/lowest) costs.
  Map<int, int> queue = {0: 0};

  for (var i in 0.to(14)) {
    print('next section - queue ${queue.length}');
    var nextMap = <int, int>{};
    for (var e in queue.entries) {
      var current = e.key;
      var c0 = e.value * 10;
      for (var d in 1.to(10)) {
        var c = c0 + d;
        var endState = runSectionNumber(i, d, current);

        // Only keep track of the identical states that were most
        // expensive to create.
        if (!mn && (nextMap[endState] ?? 0) < c) {
          nextMap[endState] = c;
        } else {
          if ((nextMap[endState] ?? maxSafeInteger) > c) {
            nextMap[endState] = c;
          }
        }
      }
    }
    queue = nextMap;
  }
  // We now have a list of final state Nodes.
  var good = queue.keys.where((e) => e == 0);
  var cost =
      mn ? good.map((e) => queue[e]).min() : good.map((e) => queue[e]).max();
  return cost!;
}

int runSectionNumber(int sn, int digit, int z) {
  int w = digit;
  List<int> p = params[sn];
  var x = z % 26;
  z = z ~/ p[0];
  x += p[1];
  x = (x != w) ? 1 : 0;
  var y = x == 1 ? 26 : 1;
  z *= y;
  y = w + p[2];
  y *= x;
  z += y;
  return z;
}

main() {
  var lines = File('data/data24_01.txt').readAsLinesSync();
  var t = DateTime.now();
  buildParams(lines);
  print(buildNodes()); // 93499629698999
  print(buildNodes(true)); // 11164118121471
  print('${DateTime.now().difference(t).inMilliseconds} milliseconds');
}