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public class SudokuSolver {
    public void solveSudoku(char[][] board) {
        solve(board);
    }

    private boolean solve(char[][] board) {
        for (int i = 0; i < 9; i++) {
            for (int j = 0; j < 9; j++) {
                if (board[i][j] == '*') {
                    for (char num = '1'; num <= '9'; num++) {
                        if (isValid(board, i, j, num)) {
                            board[i][j] = num;
                            if (solve(board)) {
                                return true;
                            } else {
                                board[i][j] = '*'; // 回溯 Backtrack
                            }
                        }
                    }
                    return false; // No valid number found
                }
            }
        }
        return true; // All cells filled
    }

    private boolean isValid(char[][] board, int row, int col, char num) {
        for (int i = 0; i < 9; i++) {
            if (board[row][i] == num || board[i][col] == num || board[3 * (row / 3) + i / 3][3 * (col / 3) + i % 3] == num) {
                return false;
            }
        }
        return true;
    }

    public static void main(String[] args) {
        char[][] board = {
            {'*','4','*',  '*','*','3',  '*','*','1'},
            {'3','*','*',  '5','*','*',  '*','9','*'},
            {'*','*','6',  '*','7','*',  '*','*','*'},

            {'*','2','*',  '*','8','4',  '*','*','*'},
            {'*','*','*',  '*','6','*',  '*','4','*'},
            {'*','*','7',  '*','*','*',  '*','5','*'},

            {'2','*','*',  '6','*','*',  '9','*','*'},
            {'*','*','*',  '*','*','*',  '4','*','*'},
            {'9','*','5',  '1','*','*',  '*','*','2'}
        };
      //  char[][] board = {
      //       {'*','*','*',  '*','*','*',  '*','*','*'},
      //       {'*','*','*',  '*','*','*',  '*','*','*'},
      //       {'*','*','*',  '*','*','*',  '*','*','*'},

      //       {'*','*','*',  '*','*','*',  '*','*','*'},
      //       {'*','*','*',  '*','*','*',  '*','*','*'},
      //       {'*','*','*',  '*','*','*',  '*','*','*'},

      //       {'*','*','*',  '*','*','*',  '*','*','*'},
      //       {'*','*','*',  '*','*','*',  '*','*','*'},
      //       {'*','*','*',  '*','*','*',  '*','*','*'}
      //  };

        SudokuSolver solver = new SudokuSolver();
        solver.solveSudoku(board);

        for (int i = 0; i < 9; i++) {
            for (int j = 0; j < 9; j++) {
                System.out.print(board[i][j] + " ");
            }
            System.out.println();
        }
    }
}