This is a game for smart guys! IF you have know this then ignore the content below. Or not you can just google it first.
You have to calculate all the numbers that possibility to fill the blank.
Sudoku is a logic-based number placement puzzle.Starting with a partially completed 9x9 grid, the objective is to fill the grid so that each row, each column, and each of the 3x3 boxes(also called blocks<) contains the digits 1 to 9 exactly once.