Allow Swaps only if tiles are next to each other

lib/main.dart

@@ -7,6 +7,7 @@ void main() {
 
 class MyApp extends StatelessWidget {
   const MyApp({super.key});
+
   final int gridSize = 12;
 
   // This widget is the root of your application.
@@ -69,7 +70,8 @@ class _MyHomePageState extends State<MyHomePage> {
   }
 
   void _initializeGrid() {
-    _grid = List.generate(widget.gridSize, (_) => List.generate(widget.gridSize, (_) => Random().nextInt(5)));
+    _grid = List.generate(widget.gridSize,
+        (_) => List.generate(widget.gridSize, (_) => Random().nextInt(5)));
   }
 
   @override
@@ -124,17 +126,29 @@ class _MyHomePageState extends State<MyHomePage> {
   }
 
   void _onTileTap(int row, int col) {
-      setState(() {
-        if (_selectedRow == -1 && _selectedCol == -1) {
-          _selectedRow = row;
-          _selectedCol = col;
-        } else {
+    setState(() {
+      if (_selectedRow == -1 && _selectedCol == -1) {
+        _selectedRow = row;
+        _selectedCol = col;
+      } else {
+        if (_isValidMove(_selectedRow, _selectedCol, row, col)) {
           _swapTiles(_selectedRow, _selectedCol, row, col);
-          _selectedRow = -1;
-          _selectedCol = -1;
         }
-      });
+        _selectedRow = -1;
+        _selectedCol = -1;
+      }
+    });
   }
+
+  bool _isValidMove(int row1, int col1, int row2, int col2) {
+    // Check if the two tiles are adjacent
+    if ((row1 == row2 && (col1 - col2).abs() == 1) ||
+        (col1 == col2 && (row1 - row2).abs() == 1)) {
+      return true;
+    }
+    return false;
+  }
+
   void _swapTiles(int row1, int col1, int row2, int col2) {
     int temp = _grid[row1][col1];
     _grid[row1][col1] = _grid[row2][col2];