Sudoku Definition:
1. No row has the same number.
2. No column has the same number.
3. The grid can be divided into 9 smaller grids(thick line width border) where they do not have the same number.

Brute force method: This method tries a number from 1 to 9 for each blank cell until it does not violate Sudoku definition. When this happens, it goes to next blank cell. If none of 9 numbers work, it falls back to the previous blank cell.

数独-暴力法定义：
1）没有行包含两个相同的数字。
2）没有列包含两个相同的数字。
3）从左上角开始，网格中有9个3x3面板。3x3面板不能包含两个相同的数字。