Completed puzzles are always a type of Latin square with an additional constraint on the contents of individual regions. For example, the same single integer may not appear twice in the same 9x9 playing board row or column or in any of the nine 3x3 subregions of the 9x9 playing board.[4]
The puzzle was popularized in 1986 by the Japanese puzzle company Nikoli, under the name Sudoku, meaning single number.[5] It became an international hit in 2005.[6]
