sudoku (addicted game; please do not try)

Sudoku is a logic-based number placement puzzle. The objective is to fill a 9x9 grid so that each column, each row, and each of the nine 3x3 boxes (also called blocks or regions) contains the digits from 1 to 9. The puzzle setter provides a partially completed grid.
Completed Sudoku puzzles are a type of Latin square, with an additional constraint on the contents of individual regions. Leonhard Euler is sometimes incorrectly cited as the source of the puzzle, based on his work with Latin squares.[1]
The modern puzzle was invented by an American, Howard Garns, in 1979 and published by Dell Magazines under the name "Number Place".[2] It became popular in Japan in 1986, after it was published by Nikoli and given the name Sudoku, meaning single number.