Add day 3

flake.nix

@@ -0,0 +1,26 @@
+{
+    description = "Advent of Code 2023";
+    inputs = {
+        flake-utils.url = "github:numtide/flake-utils";
+        nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
+    };
+
+    outputs = {
+        self,
+        nixpkgs,
+        flake-utils,
+    }: flake-utils.lib.eachDefaultSystem (system:
+    let pkgs = nixpkgs.legacyPackages.${system}; in
+    {
+        devShells = { default = pkgs.mkShell {
+          buildInputs = with pkgs; [
+            (with dotnetCorePackages;
+              combinePackages [
+                dotnet-sdk_8
+                dotnetPackages.Nuget
+              ])
+          ] ++ [pkgs.swift darwin.apple_sdk.frameworks.Foundation darwin.apple_sdk.frameworks.CryptoKit darwin.apple_sdk.frameworks.GSS pkgs.zlib pkgs.zlib.dev pkgs.openssl pkgs.icu];
+        };};
+    }
+    );
+}