Add undo functionality

Implemented an undo move feature for the subtraction game, allowing users to revert their last action.

src/components/SubtractionGame.tsx

@@ -19,6 +19,11 @@ const SubtractionGame: React.FC<SubtractionGameProps> = ({ showSocialShare = tru
   const [winner, setWinner] = useState<string | null>(null);
   const [highlightedIndices, setHighlightedIndices] = useState<number[]>([]);
   const [hoveredIndex, setHoveredIndex] = useState<number | null>(null);
+  const [previousGameState, setPreviousGameState] = useState<{
+    removedCircles: Set<number>;
+    removedByPlayer: Map<number, 'Lata' | 'Raj'>;
+    currentPlayer: 'Lata' | 'Raj';
+  } | null>(null);
 
   // Update k slider max when n changes
   useEffect(() => {
@@ -49,6 +54,7 @@ const SubtractionGame: React.FC<SubtractionGameProps> = ({ showSocialShare = tru
     setGameStarted(true);
     setCurrentPlayer('Lata');
     setWinner(null);
+    setPreviousGameState(null);
   };
 
   const resetGame = () => {
@@ -60,6 +66,7 @@ const SubtractionGame: React.FC<SubtractionGameProps> = ({ showSocialShare = tru
     setCurrentPlayer('Lata');
     setHighlightedIndices([]);
     setHoveredIndex(null);
+    setPreviousGameState(null);
   };
 
   const handleCircleClick = (index: number) => {
@@ -67,6 +74,13 @@ const SubtractionGame: React.FC<SubtractionGameProps> = ({ showSocialShare = tru
       return;
     }
 
+    // Store current state before making the move
+    setPreviousGameState({
+      removedCircles: new Set(removedCircles),
+      removedByPlayer: new Map(removedByPlayer),
+      currentPlayer
+    });
+
     // Mark all circles from clicked index onwards as removed
     const newRemovedCircles = new Set(removedCircles);
     const newRemovedByPlayer = new Map(removedByPlayer);
@@ -100,6 +114,15 @@ const SubtractionGame: React.FC<SubtractionGameProps> = ({ showSocialShare = tru
     setCurrentPlayer(currentPlayer === 'Lata' ? 'Raj' : 'Lata');
   };
 
+  const undoLastMove = () => {
+    if (!previousGameState) return;
+    
+    setRemovedCircles(previousGameState.removedCircles);
+    setRemovedByPlayer(previousGameState.removedByPlayer);
+    setCurrentPlayer(previousGameState.currentPlayer);
+    setPreviousGameState(null);
+  };
+
   const getBackgroundColor = () => {
     if (!gameStarted || winner) return 'bg-background';
     return currentPlayer === 'Lata' ? 'bg-blue-100 dark:bg-blue-950' : 'bg-purple-100 dark:bg-purple-950';
@@ -172,7 +195,7 @@ const SubtractionGame: React.FC<SubtractionGameProps> = ({ showSocialShare = tru
               </div>
             </div>
 
-            <div className="text-center">
+            <div className="flex justify-center gap-4">
               <Button
                 onClick={gameStarted ? resetGame : startGame}
                 size="lg"
@@ -180,6 +203,17 @@ const SubtractionGame: React.FC<SubtractionGameProps> = ({ showSocialShare = tru
               >
                 {gameStarted ? 'Reset' : 'Play'}
               </Button>
+              
+              {gameStarted && !winner && previousGameState && (
+                <Button
+                  onClick={undoLastMove}
+                  variant="outline"
+                  size="lg"
+                  className="px-6"
+                >
+                  Undo Last Move
+                </Button>
+              )}
             </div>
           </div>