Project-AOC-2024/Day3/Program.cs

using System.Text.RegularExpressions;

var memory = File.ReadAllText("input.txt");
var result = ParseCorruptedMemory(memory);
var resultPart2 = ParseCorruptedMemoryPart2(memory);
Console.WriteLine($"Part1: {result}\nPart2: {resultPart2}");

int ParseCorruptedMemory(string corruptedMemory)
{
    var mulPattern = @"mul\s*\(\s*(\d+)\s*,\s*(\d+)\s*\)";
    var matches = Regex.Matches(corruptedMemory, mulPattern);
    
    var totalSum = matches
        .Select(match => 
        {
            var x = int.Parse(match.Groups[1].Value);
            var y = int.Parse(match.Groups[2].Value);
            
            return x * y;
        }).Sum();
        
    return totalSum;
}

int ParseCorruptedMemoryPart2(string corruptedMemory)
{
    var mulPattern = @"mul\s*\(\s*(\d+)\s*,\s*(\d+)\s*\)";
    var doPattern = @"do\s*\(\s*\)";
    var dontPattern = @"don't\s*\(\s*\)";
    
    var mulEnabled = true;
    var mulMatches = Regex.Matches(corruptedMemory, mulPattern);
    var doMatches = Regex.Matches(corruptedMemory, doPattern);
    var dontMatches = Regex.Matches(corruptedMemory, dontPattern);
    
    var allMatches = mulMatches
        .Concat(doMatches)
        .Concat(dontMatches)
        .OrderBy(m => m.Index)
        .ToList();
    
    var results = new List<int>();
        
    foreach (var match in allMatches)
    {
        if (Regex.IsMatch(match.Value, doPattern))
        {
            mulEnabled = true;
        }
        else if (Regex.IsMatch(match.Value, dontPattern))
        {
            mulEnabled = false;
        }
        else if (Regex.IsMatch(match.Value, mulPattern) && mulEnabled)
        {
            var x = int.Parse(match.Groups[1].Value);
            var y = int.Parse(match.Groups[2].Value);
            results.Add(x * y);
        }
    }
        
    return results.Sum();
}