Initial Days

Day3/Day3.csproj

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+<Project Sdk="Microsoft.NET.Sdk">
+
+    <PropertyGroup>
+        <OutputType>Exe</OutputType>
+        <TargetFramework>net9.0</TargetFramework>
+        <ImplicitUsings>enable</ImplicitUsings>
+        <Nullable>enable</Nullable>
+    </PropertyGroup>
+
+    <ItemGroup>
+      <None Update="input.txt">
+        <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
+      </None>
+    </ItemGroup>
+
+</Project>

Day3/Program.cs

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+using System.Text.RegularExpressions;
+// string input = "xmul(2,4)&mul[3,7]!^don't()_mul(5,5)+mul(32,64](mul(11,8)undo()?mul(8,5))";
+string input = File.ReadAllText("input.txt").ReplaceLineEndings("");
+int total = 0;
+
+Regex valid = new Regex("mul\\((?<x>[0-9]+),(?<y>[0-9]+)\\)");
+Regex dontandDo = new Regex("(don\\'t\\(\\).*?do\\(\\))");
+
+input = dontandDo.Replace(input, "");
+
+List<(int x, int y)> multiplies = new();
+
+foreach (Match match in valid.Matches(input))
+{
+    string x = match.Groups["x"].Value;
+    string y = match.Groups["y"].Value;
+    multiplies.Add((int.Parse(x), int.Parse(y)));
+}
+
+foreach ((int x, int y) in multiplies)
+{
+    total += x * y;
+}
+
+Console.WriteLine(total);