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Sudoku

A Sudoku puzzle...
...and its solution numbers marked in red.

Sudoku (数独) is a logic-based number-placement puzzle. The objective is to fill a 9×9 grid so that each column, each row, and each of the nine 3×3 boxes (also called blocks or regions) contains the digits from 1 to 9 only one time each. The puzzle setter provides a partially completed grid.

Completed puzzles are usually 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 related work with Latin squares.

The modern puzzle was invented by an American architect, Howard Garns, in 1979 and published by Dell Magazines under the name "Number Place". It was popularized in 1986 by the Japanese puzzle company Nikoli under the name Sudoku, meaning single number. It became an international hit in 2005.

Source:Wikipedia