Sudoku which was earlier known as Suuji wa dokushin ni kagiru (the numbers
must occur only once) is the most well-liked number puzzle worldwide. The aim
of the puzzle is to put a number from 1 up to 9 to each grid. The grids include
one large 9x9 grid that have nine 3x3 smaller grids. Each row, column, and region
must contain only one instance of each number.

Sudoku originally circulated in 1979 by Dell Puzzle Magazines under the title
The Number Place but has become first popular in Japan when it was adopted
and published in Nikolist newspaper in 1984.

In 1986, the number of givens was limited to no more than 32 and the givens
were now distributed in rotationally symmetric cells.

It was in 1989 when the DigitHunt on the Commodore 64, the first home computer
version of Sudoku was released by Loadstar/Softdisk Publishing.

Then later in 1995, a computerized puzzle generator for Macintosh with a
name of Single Number was created by Yoshimitsu Kanai. A computerized puzzle
generator was also created after a year for PDA and last year, a version for
Mac OS-X was released.

Nowadays, because of the phenomenal fame of this number puzzle, there are
so many variations of the originally 9x9 grid Sudoku puzzle, that are virtually
available anywhere. There are variations named as Logi-5 with 5×5 grids
with pentomino regions. The World Puzzle Championship has also featured a
6×6 grid with 2×3 regions and a 7×7 grid with six heptomino
regions and a disjoint region.

Other variations are The Daily SuDoku for Kids that features 4×4, 6×6,
and simpler 9×9 grids; the jigsaw variation which is a 9x9 grid with
nonomino regions; and the Sudoku used in 2005 US Puzzle Championship with
parallelogram regions that wrapped around the outer border of the puzzle.

There are also several larger grids of Sudoku such as the 12×12-grid
Monster SuDoku, the 12×12-grid Dodeka Sudoku with 12 regions each being
4×3, the16×16 Number Place Challenger Puzzles of Dell and the
25×25 Sudoku named the Giant behemoths from Nikolis.The Super Sudoku
X of the Daily Mail is an an 8×8 grid in which rows, columns, main diagonals,
2×4 blocks and 4×2 blocks contain each number once. These puzzles
are typically printed in colour, with each disjoint group using one colour
for clarity

Chess-themed variants were also created wherein certain numbers are replaced
with chess pieces, whose attack ranges are translated into extra regions and/or
additional position boundaries. Any of these ways of adding restrictions or
limitations tends to decrease the number of givens required to make a puzzle
valid. There is even more difficult version of Sudoku called the Dion Cube,
a 3-dimensional version of 16x16 squares which include letters as well as
numbers.

Other variations of extra restrictions are arithmetical in nature, requiring
the numbers in delineated segments of the grid to have specific sums or products.
Some such variants totally forsake standard givens. Magic Sudoku adds some
restrictions to the standard Sudoku to solve it with fewer numbers.

Alphabetical variations have also emerged over time. There is no functional
difference in the puzzle except when the letters spell something. Some variants,
such as in the TV Guide, include a word reading along a main diagonal, row,
or column once solved; determining the word in advance can be viewed as a
solving aid. The Code Doku has an entire sentence implanted into the puzzle.
The Super Wordoku from Top Notch implants two 9-letter words, one on each
diagonal. It is doubtful whether these are true Sudoku puzzles because they
have a single linguistically valid solution but these puzzles cannot be solved
entirely by logic. It requires the player to determine the implanted words.

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