Although the 9×9 grid with 3×3 regions is by far the most common, many variations exist. Sample puzzles can be 4×4 grids with 2×2 regions; 5×5 grids with pentomino regions have been published under the name

*Logi-5*; the World Puzzle Championship has featured a 6×6 grid with 2×3 regions and a 7×7 grid with six heptomino regions and a disjoint region. Larger grids are also possible. The

*Times*offers a 12×12-grid

*Dodeka sudoku*with 12 regions of 4×3 squares. Dell regularly publishes 16×16

*Number Place Challenger*puzzles (the 16×16 variant often uses 1 through G rather than the 0 through F used in hexadecimal). Nikoli offers 25×25

*Sudoku the Giant*behemoths.

*Sudoku-zilla*,

^{[12]}a 100×100-grid was published in print in 2010.

Another common variant is to add limits on the placement of numbers beyond the usual row, column, and box requirements. Often the limit takes the form of an extra "dimension"; the most common is to require the numbers in the main diagonals of the grid also to be unique. The aforementioned

*Number Place Challenger*puzzles are all of this variant, as are the

*Sudoku X*puzzles in the

*Daily Mail*, which use 6×6 grids. The

*Sudoku X4*family of iPhone/iPad apps combine this "X" varation with the

*Sunday Telegraph*-style interlocking colored nonomino or Jigsaw shapes of nine spaces each instead of the 3x3 regions, providing a total of four different kinds of puzzles.

### [edit] Mini Sudoku

A variant named "Mini Sudoku" appears in the American newspaper*USA Today*and elsewhere, which is played on a 6×6 grid with 3×2 regions. The object is the same as standard Sudoku, but the puzzle only uses the numbers 1 through 6. A similar form, for younger solvers of puzzles, called "The Junior Sudoku", has appeared in some newspapers, such as some editions of The Daily Mail.

### [edit] Cross Sums Sudoku

Another variant is the combination of Sudoku with Kakuro on a 9×9 grid, called Cross Sums Sudoku, in which clues are given in terms of cross sums. The clues can also be given by cryptic alphametics in which each letter represents a single digit from 0 to 9. An example is NUMBER+NUMBER=KAKURO which has a unique solution 186925+186925=373850. Another example is SUDOKU=IS×FUNNY whose solution is 426972=34×12558.Killer Sudoku

Main article: Killer Sudoku

The Killer Sudoku variant combines elements of **Sudoku**and Kakuro.

### [edit] Alphabetical Sudoku

Alphabetical variations have emerged, sometimes called**Wordoku**; there is no functional difference in the puzzle unless 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. A Wordoku might contain other words, other than the main word.

### [edit] Hypersudoku

Hypersudoku is one of the most popular variants. It is published by newspapers and magazines around the world and is also known as "NRC Sudoku," "Windoku," "Hyper-Sudoku" and "4 Square Sudoku." The layout is identical to a normal Sudoku, but with additional interior areas defined in which the numbers 1 to 9 must appear. The solving algorithm is slightly different from the normal Sudoku puzzles because of the leverage on the overlapping squares. This overlap gives the player more information to logically reduce the possibilities in the remaining squares. The approach to playing is similar to Sudoku but with possibly more emphasis on scanning the squares and overlap rather than columns and rows.Puzzles constructed from multiple Sudoku grids are common. Five 9×9 grids which overlap at the corner regions in the shape of a quincunx is known in Japan as Gattai 5 (five merged) Sudoku. In

*The Times*,

*The Age*and

*The Sydney Morning Herald*this form of puzzle is known as

*Samurai SuDoku*. The

*Baltimore Sun*and the

*Toronto Star*publish a puzzle of this variant (titled

*High Five*) in their Sunday edition. Often, no givens are to be found in overlapping regions. Sequential grids, as opposed to overlapping, are also published, with values in specific locations in grids needing to be transferred to others.

Str8ts shares the Sudoku requirement of uniqueness in the rows and columns but the third constraint is very different. Str8ts uses black cells (some with clue numbers) to divide the board into compartments. These must be filled with a set of numbers that form a "straight," like the poker hand. A straight is a set of numbers with no gaps in them, such as "4,3,6,5"—and the order can be non-sequential. 9×9 is the traditional size but with suitable placement of black cells any size board is possible.

A tabletop version of Sudoku can be played with a standard 81-card Set deck (see Set game). A three-dimensional Sudoku puzzle was invented by Dion Church and published in the

*Daily Telegraph*in May 2005.

*The Times*also publishes a three-dimensional version under the name Tredoku. There is a Sudoku version of the Rubik's Cube named Sudoku Cube.

There are many other variants. Some are different shapes in the arrangement of overlapping 9×9 grids, such as butterfly, windmill, or flower.

^{[13]}Others vary the logic for solving the grid. One of these is Greater Than Sudoku. In this a 3×3 grid of the Sudoku is given with 12 symbols of Greater Than (>) or Less Than (<) on the common line of the two adjacent numbers.

^{[10]}Another variant on the logic of solution is Clueless Sudoku, in which nine 9×9 Sudoku grids are themselves placed in a three-by-three array. The center cell in each 3×3 grid of all nine puzzles is left blank and form a tenth Sudoku puzzle without any cell completed; hence, "clueless".

^{[13]}

#### [edit] Duidoku

Duidoku is a two player variant of Sudoku. It is played on a 4X4 board i.e. 16 squares or four clusters each containing four squares.The game is followed using the rules of Sudoku. Four numbers are used, and each player consecutively places one number out of the four such that he or she makes no illegal moves. The first player to make an illegal move loses.

^{[14]}

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