private static final int SIZE = 9;  // Size of the Sudoku gridprivate JTextField[][] grid = new JTextField[SIZE][SIZE];  // 9x9 JTextFields for the gridprivate int[][] board = new int[SIZE][SIZE];  // Sudoku boardpublic SudokuUI() {    setTitle("Sudoku Solver");    setSize(600, 600);    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);    setLayout(new BorderLayout());    // Create the Sudoku grid panel    JPanel gridPanel = new JPanel(new GridLayout(SIZE, SIZE));    for (int row = 0; row < SIZE; row++) {        for (int col = 0; col < SIZE; col++) {            grid[row][col] = new JTextField();            grid[row][col].setHorizontalAlignment(JTextField.CENTER);            grid[row][col].setFont(new Font("Arial", Font.BOLD, 20));            grid[row][col].setBorder(BorderFactory.createLineBorder(Color.BLACK));            gridPanel.add(grid[row][col]);        }    }    // Button panel with "Solve" button    JPanel buttonPanel = new JPanel();    JButton solveButton = new JButton("Solve");    solveButton.setFont(new Font("Arial", Font.BOLD, 16));    solveButton.addActionListener(new ActionListener() {        @Override        public void actionPerformed(ActionEvent e) {            solveSudoku();        }    });    buttonPanel.add(solveButton);    // Add panels to the frame    add(gridPanel, BorderLayout.CENTER);    add(buttonPanel, BorderLayout.SOUTH);}// Parse the Sudoku grid from the UI into the board arrayprivate void parseInput() {    for (int row = 0; row < SIZE; row++) {        for (int col = 0; col < SIZE; col++) {            String text = grid[row][col].getText();            if (text.isEmpty()) {                board[row][col] = 0;  // Empty cells are represented as 0            } else {                board[row][col] = Integer.parseInt(text);            }        }    }}// Display the solved Sudoku on the UIprivate void displaySolution() {    for (int row = 0; row < SIZE; row++) {        for (int col = 0; col < SIZE; col++) {            grid[row][col].setText(String.valueOf(board[row][col]));        }    }}// Solve the Sudoku using the existing solver algorithmprivate void solveSudoku() {    parseInput();  // Parse the UI input into the board array    // Create an instance of the Sudoku solver with the current board    SudokuOptimized solver = new SudokuOptimized(board);    if (solver.solve()) {        displaySolution();  // Display the solution on the UI        JOptionPane.showMessageDialog(this, "Sudoku Solved!");    } else {        JOptionPane.showMessageDialog(this, "Unsolvable Sudoku");    }}public static void main(String[] args) {    // Create and display the Sudoku UI    SwingUtilities.invokeLater(new Runnable() {        @Override        public void run() {            SudokuUI sudokuUI = new SudokuUI();            sudokuUI.setVisible(true);        }    });}

private int[][] board;public static final int EMPTY = 0;public static final int SIZE = 9;public SudokuOptimized(int[][] board) {    this.board = board;}// Check if a number can be placed at a specific cellprivate boolean isSafe(int row, int col, int num) {    int boxRowStart = row - row % 3;    int boxColStart = col - col % 3;    for (int i = 0; i < SIZE; i++) {        if (board[row][i] == num || board[i][col] == num ||             board[boxRowStart + i / 3][boxColStart + i % 3] == num) {            return false;        }    }    return true;}// Find the next empty cell (used for backtracking)private int[] findNextEmptyCell() {    for (int row = 0; row < SIZE; row++) {        for (int col = 0; col < SIZE; col++) {            if (board[row][col] == EMPTY) {                return new int[] {row, col};            }        }    }    return null;}// Solve the Sudoku using backtrackingpublic boolean solve() {    int[] emptyCell = findNextEmptyCell();    if (emptyCell == null) return true;  // No empty cell, puzzle solved    int row = emptyCell[0];    int col = emptyCell[1];    for (int num = 1; num <= SIZE; num++) {        if (isSafe(row, col, num)) {            board[row][col] = num;            if (solve()) return true;            board[row][col] = EMPTY;        }    }    return false;}