Sudoku

代码说明：

  Player fills a number from 1 to 9 into given empty space with a rule that no number is appear twice in a single row, column, and minigrid. To play a game of Sudoku, click PlayGame button and an incomplete board of Sudoku will be created in the grid box. Use CheckBoard button to check whether there is a violation in the board. To solve an incomplete Sudoku board, fill the grid box with the corresponding number and click SolveSudoku button. Remember to click ResetBoard before starting a new game or entering an incomplete board to be solved.