# Rule of sudoku

**Sudoku**, also called **Number Place**, is a logic-based number-placement puzzle. A problem of sudoku puzzle is made of 9x9 grid with digits from 1 to 9 partially filled as in the following figure.

Objective of the sudoku is to fill in the blank cells with numbers 1 to 9, so that each **row**, **column**, and **box** (3x3 subgrids as indicated in bold lines in the figure) contains all of the digits from 1 to 9.

Solution of the above puzzle is as follows. Please confirm that the condition is satisfied.

Sudoku puzzle should have a unique solution.

## Variant

The above mentioned rule is a standard sudoku rule adopted in Kaidoku program. There are many variant of the rule. For detail, please refer to