invalid choice dialog

lib/super.dart

@@ -72,6 +72,19 @@ class _SuperGameState extends State<SuperGame> {
               turn: turn,
               cellOnTapCallback: (int i) {
                 if (!_checkValidChoice(data[subGame], i)) {
+                  showDialog(
+                      context: context,
+                      builder: (context) => AlertDialog(
+                            content:
+                                Text("${data[subGame][i].name.toUpperCase()}"
+                                    " already claimed "
+                                    "[${i % 3}, ${(i / 3).floor()}]"),
+                            actions: [
+                              ElevatedButton(
+                                  onPressed: () => Navigator.pop(context),
+                                  child: const Text("Close"))
+                            ],
+                          ));
                   return;
                 }