Add Day 3

Day3/Program.cs

@@ -0,0 +1,65 @@
+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.Cast<Match>())
+        .Concat(dontMatches.Cast<Match>())
+        .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 mulMatch = (Match)match;
+            var x = int.Parse(mulMatch.Groups[1].Value);
+            var y = int.Parse(mulMatch.Groups[2].Value);
+            results.Add(x * y);
+        }
+    }
+        
+    return results.Sum();
+}