Origin
Sudoku is said to have 18 - century roots, but the trace is non conclusive.
The link of Sudoku to Japan was traced to Japanese publisher Nikoli, who claims it brought the puzzle to Japan from the United States, which was then simply called Number Place.
Rules
Fill in the grid so that every row, every column, and every 3x3 box contains the digits 1 through 9
That's all there is to it.
Help
Click on a number in the header to mark all the fields containing that number.
Ctrl+click on a field to change its background color.
Ctrl+click again to change it again.
Tips
You can enter more than one number in a box.
It's much harder than it seems, don't give up too easily.