adventofcode2025/lib/day3/command.dart

import "dart:convert";
import "dart:io";

import "package:args/command_runner.dart";

class Day3Command extends Command {
  // The [name] and [description] properties must be defined by every
  // subclass.
  @override
  final name = "day3";

  @override
  final description = "Run Advent of Code 2025 Day 3";

  Day3Command() {
    // we can add command specific arguments here.
    // [argParser] is automatically created by the parent class.
  }

  // [run] may also return a Future.
  @override
  Future<void> run() async {
    // [argResults] is set before [run()] is called and contains the flags/options
    // passed to this command.

    if (argResults!.rest.length != 1) {
      print(
        "Expected 1 positional arguments, found ${argResults!.rest.length}",
      );
    }
    var filePath = argResults!.rest[0];

    print("Parsing file: $filePath");

    var inputFile = File(filePath);
    var part1Result = await inputFile
        .openRead()
        .transform(utf8.decoder)
        .transform(LineSplitter())
        .map((line) {
          int tens = -1;
          int ones = -1;
          final chars = line.split("");

          for (final (idx, char) in chars.indexed) {
            final charAsInt = int.parse(char);
            if (charAsInt > tens && idx < chars.length - 1) {
              tens = charAsInt;
              ones = -1;
            } else if (charAsInt > ones) {
              ones = charAsInt;
            }
          }

          return tens * 10 + ones;
        })
        .reduce((left, right) => left + right);

    print("Part 1 Answer: $part1Result");

    var part2Result = await inputFile
        .openRead()
        .transform(utf8.decoder)
        .transform(LineSplitter())
        .map((line) {
          int resultLength = 12;
          var resultList = List.generate(
            resultLength,
            (i) => 0,
            growable: false,
          );
          final chars = line.split("");

          for (final (charIdx, char) in chars.indexed) {
            final charAsInt = int.parse(char);
            var charsLeftInStream = chars.length - charIdx - 1;
            for (final (placeIdx, placeValue) in resultList.indexed) {
              var placesLeft = resultList.length - placeIdx - 1;
              if (placesLeft > charsLeftInStream) {
                continue;
              }
              if (charAsInt > placeValue) {
                resultList[placeIdx] = charAsInt;
                resultList.fillRange(placeIdx + 1, resultList.length, 0);
                break;
              }
            }
          }

          int result = 0;
          for (final placeValue in resultList) {
            result *= 10;
            result += placeValue;
          }

          return result;
        })
        .reduce((left, right) => left + right);

    print("Part 2 Answer: $part2Result");
  }
}