This is a basic Number Place game.
- The same single integer may not appear twice
1. in the same 9x9 playing board row
2. in the same 9x9 playing board column
3. in any of the nine 3x3 subregions of the 9x9 playing board.
* Included 2,000 problems.
* Resume suspended problem.
* The selected number is displayed at green.
* The repeated number is displayed at red.
* You can change the background color.
* The world ranking of number of clear issues