Added some basic logic to remove created matches and apply gravity so new blocks fall down

lib/main.dart

@@ -1,4 +1,5 @@
 import 'dart:math';
+
 import 'package:flutter/material.dart';
 
 void main() {
@@ -72,6 +73,15 @@ class _MyHomePageState extends State<MyHomePage> {
   void _initializeGrid() {
     _grid = List.generate(widget.gridSize,
         (_) => List.generate(widget.gridSize, (_) => Random().nextInt(5)));
+    _removeInitialMatches();
+  }
+
+  void _removeInitialMatches() {
+    bool hasMatches;
+    do {
+      hasMatches = _removeMatches();
+      _applyGravity();
+    } while (hasMatches);
   }
 
   @override
@@ -133,6 +143,9 @@ class _MyHomePageState extends State<MyHomePage> {
       } else {
         if (_isValidMove(_selectedRow, _selectedCol, row, col)) {
           _swapTiles(_selectedRow, _selectedCol, row, col);
+          while (_removeMatches()) {
+            _applyGravity();
+          }
         }
         _selectedRow = -1;
         _selectedCol = -1;
@@ -141,14 +154,96 @@ class _MyHomePageState extends State<MyHomePage> {
   }
 
   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;
+      int temp = _grid[row1][col1];
+      _grid[row1][col1] = _grid[row2][col2];
+      _grid[row2][col2] = temp;
+
+      bool isValid = _findMatches(row1, col1).isNotEmpty ||
+          _findMatches(row2, col2).isNotEmpty;
+
+      _grid[row2][col2] = _grid[row1][col1];
+      _grid[row1][col1] = temp;
+
+      return isValid;
     }
     return false;
   }
 
+  List<List<int>> _findMatches(int row, int col) {
+    int color = _grid[row][col];
+    List<List<int>> matches = [];
+
+    // Check horizontally
+    List<int> horizontalMatch = [];
+    for (int c = col; c >= 0 && _grid[row][c] == color; c--) {
+      horizontalMatch.add(c);
+    }
+    for (int c = col + 1; c < widget.gridSize && _grid[row][c] == color; c++) {
+      horizontalMatch.add(c);
+    }
+    if (horizontalMatch.length >= 3) {
+      for (int c in horizontalMatch) {
+        matches.add([row, c]);
+      }
+    }
+
+    // Check vertically
+    List<int> verticalMatch = [];
+    for (int r = row; r >= 0 && _grid[r][col] == color; r--) {
+      verticalMatch.add(r);
+    }
+    for (int r = row + 1; r < widget.gridSize && _grid[r][col] == color; r++) {
+      verticalMatch.add(r);
+    }
+    if (verticalMatch.length >= 3) {
+      for (int r in verticalMatch) {
+        matches.add([r, col]);
+      }
+    }
+
+    return matches;
+  }
+
+  bool _removeMatches() {
+    List<List<int>> allMatches = [];
+
+    for (int row = 0; row < widget.gridSize; row++) {
+      for (int col = 0; col < widget.gridSize; col++) {
+        List<List<int>> matches = _findMatches(row, col);
+        if (matches.isNotEmpty) {
+          allMatches.addAll(matches);
+        }
+      }
+    }
+
+    for (var match in allMatches) {
+      _grid[match[0]][match[1]] = -1; // Mark the tile as removed
+    }
+
+    return allMatches.isNotEmpty;
+  }
+
+  void _applyGravity() {
+    for (int col = 0; col < widget.gridSize; col++) {
+      int emptyRow = widget.gridSize - 1;
+      for (int row = widget.gridSize - 1; row >= 0; row--) {
+        if (_grid[row][col] != -1) {
+          _grid[emptyRow][col] = _grid[row][col];
+          if (emptyRow != row) {
+            _grid[row][col] = -1;
+          }
+          emptyRow--;
+        }
+      }
+
+      for (int row = emptyRow; row >= 0; row--) {
+        _grid[row][col] = Random().nextInt(5);
+      }
+    }
+  }
+
   void _swapTiles(int row1, int col1, int row2, int col2) {
     int temp = _grid[row1][col1];
     _grid[row1][col1] = _grid[row2][col2];