adventofcode/2024/day2/Program.cs

const int EXAMPLE_VALUE_1 = 2;
const int EXAMPLE_VALUE_2 = 4;

StreamReader inputFile;
string input;

Console.Write("Use (p)rod or (e)xample? > ");
if (Console.ReadKey().Key == ConsoleKey.E) {
    Console.WriteLine($"\nUsing example data, value should be of {EXAMPLE_VALUE_1} and {EXAMPLE_VALUE_2}");
    inputFile = File.OpenText("example.txt");
} else {
    Console.WriteLine("\nUsing production data");
    inputFile = File.OpenText("input.txt");
}
input = inputFile.ReadToEnd();

string[] reports = input.Split("\n");
List<string> invalidReports = [];
Console.WriteLine($"{reports.Length} reports will be processed");

int validReports = 0;

static bool validateReport(List<int> levels) {
    bool shouldBeIncreasing = levels[0] < levels[1];
    bool hasIgnoredZeroIndex = false;

    int lastNumber = levels[0];
    foreach(var level in levels) {
        if (levels.IndexOf(level) == 0 && !hasIgnoredZeroIndex) {
            hasIgnoredZeroIndex = true;
            continue;
        }

        if (lastNumber >= level && shouldBeIncreasing || lastNumber <= level && !shouldBeIncreasing) return false;
        if (Math.Abs(lastNumber - level) > 3) return false;

        lastNumber = level;
    }
    return true;
}

// Part 1
foreach(var report in reports) {
    string[] levelsAsString = report.Split(" ");
    List <int> levels = [];

    foreach(var levelAsString in levelsAsString) {
        levels.Add(int.Parse(levelAsString));
    }
    if (validateReport(levels)) validReports++;
    else {
        invalidReports.Add(report);
    }
}

Console.WriteLine($"Part 1: {validReports} valid reports!");

// Part 2
foreach(var report in invalidReports) {
    string[] levelsAsString = report.Split(" ");
    List <int> levels = [];

    foreach(var levelAsString in levelsAsString) {
        levels.Add(int.Parse(levelAsString));
    }

    for(var i = 0; i < levels.ToArray().Length; i++) {
        List<int> manipulatedLevels = new(levels);
        manipulatedLevels.RemoveAt(i);

        if(validateReport(manipulatedLevels)) {
            validReports++;
            break;
        }
    }

}

Console.WriteLine($"Part 2: {validReports} valid reports!");