Theme and Variations
There are many different forms of Sudoku that have developed over the last few years. Some of them are straightforward extensions on the original idea of Sudoku and others take a radical turn.
Minor Variations
Grid Size
It turns out that the regular 9x9 puzzle is just the beginning, the grid size can be any old size. You can make it smaller and simpler or larger and harder to solve by just changing the grid size. Commonly used grid sizes include 2x3 regions rather than the normal 3x3 so there are six numbers to place in the squares rather than nine and 4x4 where there are sixteen numbers. Our theory page gives more detail; there is no theoretical limit on how large the grid can be. All the same strategies are used to solve these different sized puzzles.
Sudoku Dragon can generate and solve puzzles of all these sizes along with many more.
Colors, Words, Pictures and Symbols
Sudoku is about placing things in the correct order; it is not about arithmetic. The familiar numbers 1 to 9 can be replaced with anything at all, as long as each is different from each other. So the puzzle can use a set of nine different colors, nine letters or nine picture fragments. If it uses fragments of a completed picture then one of regions (usually the central one) will show the complered picture. However you really need a program to help you play these picture puzzles as you can't easily pencil in sketches of possibilities for the missing squares!
See Also: Picture Sudoku
and Word Sudoku
Word Sudoku
If letters are used rather than numbers then hidden words can be included in the grid, often this is a nine letter word in a row or column. Here's an example of a puzzle with its solution alongside, the hidden word wordgames is in the rightmost column. This variation is very similar to the stripe version of Sudoku.
In this second Word puzzle generated by Sudoku Dragon the hidden word is in the second row. The hidden word is Diplomats.
click here Sudoku Dragon fully supports Word Sudoku. The popular grid size 9x9 is supported with a hidden nine letter word.
Jigsaw or Squiggle Sudoku
In regular Sudoku all the regions in the grid have an identical shape - a square or a rectangle. In Jigsaw Sudkou, the regions can be made different shapes, that is as long as each shape is contiguous and has the same number of squares as all the other regions. The strategies have to be changed a bit. The two-out-of-three strategy, which is so useful for regular puzzles, has to be overhauled and the shared subgroup exclusion rule needs to account for the individual pattern of overlaps in each puzzle.
In this second example puzzle generated by Sudoku Dragon the irregular regions are highlighted with different colors.
The pattern of regions is symmetric.
click here Sudoku Dragon fully supports Jigsaw Sudoku for grid sizes up to 10x10.
See Also: Jigsaw Sudoku
Neighbor Order
This is a neat idea of adding extra information that is easy to see and use. The border between two squares is used to give a hint as to which neighbor is larger. It includes a pointer to the smaller number. It is also known as 'Greater than Sudoku'. A row of 9; 8 ;7; 2; 4; 1; 6; 5; 3 has the ordering 9 > 8 > 7 > 2 < 4 > 1 < 6 > 5 > 3. This extra hint introduces a new way to solve squares. If you have a 2 and a neighbor that is smaller than this then it must be a 1, similarly an 8 with a higher square neighbor must be a 9.
Here is an example puzzle with all the orderings shown in each square's border. In this case the square Bb can be immediately solved as it has neighbors 6 > x > 4 and so x must be 5.
To make solution a little harder only some of the neighbor borders man be indicated. Often the initial grid is empty except for the neighbor ordering. This is a puzzle with the addition of number ordering and so it is not strictly Sudoku any more, a picture or color Sudoku puzzle doesn't have a concept of order of neighbors; to a purist it's not quite the same thing.
See Also: Greater-Than Sudoku
Stripe
We at Sudoku Dragon have added our own little extension to Sudoku. Optionally one group in the grid will contain the numbers in ascending order (1 to 9) or descending order (9 to 1). The stripe can be wrapped up into a region which can make it hard to spot. We have a whole page devoted to describing the stripe.
X Sudoku
Going back to Euler and the origins of Sudoku the original Magic Numbers and Latin Squares had constraints on the diagonals as well as the rows and columns. X-Sudoku or Diagonal Sudoku has the numbers 1 to 9 occurring in both the diagonals as well as the rows and columns. You can make use of this extra rule to solve squares.
In this second example puzzle generated by Sudoku Dragon a grid size of 2x5 is used (ten squares per group). The diagonal nature of the puzzle
is indicated by the diagonal marks in the unallocated squares.
click here Sudoku Dragon supports X-Sudoku. All the many grid sizes can have the diagonals as an extra group.
See Also: Sudoku X
Samurai Sudoku
Most players find keeping track of the nine numbers in a 3x3 grid an adequate challenge but others prefer a bigger puzzle to solve.
The Samurai Sudoku offers this. It provides a new feature in Sudoku puzzles - overlapping puzzles. One or more regions within a puzzle are shared with another puzzle of the same size. The normal grid size for puzzles of this type is the 21x21 square grid that contains five regular 9x9 puzzles.
Sudoku Dragon supports the Samurai variation of Sudoku at grid sizes 2x2 and 3x3.
click here Killer Sudoku
One way to extend Sudoku is to add some mathematics on top of the basic Sudoku rules. In Killer Sudoku the standard grid is divided up into collections, in the top left square of the collection is the sum of the numbers that go in the squares making up the group. This lets you solve squares in new ways, in the simplest case you could have a collection of only two squares, if the sum is 3 then you know one square in 1 and the other 2, or if the sum was 17 then they must be 8 and 9. So the sum is giving extra information about the numbers in the squares quite apart from the standard 'number unique to a group' coming from Sudoku. A key starting point is to look for collections with a low average (e.g. a total of 6 for 3 squares, average 2, means can only be {1, 2, 3}) or a high average (e.g. a total of 30 for 4 squares, average 7.5 means can only be {6,7,8,9}) Usually the extra information is sufficient to start off with an empty grid and yet still be able to solve it.
See Also: Killer Sudoku
Other Variations
There are a host of other variations on the basic theme and new ones are being invented all the time. If you have found one that you like let us know about it.
Give our SudokuDragon puzzle solver a free 23 day trial by visiting our download page.
All the main Sudoku strategies have clear, easy to follow guide tutorials.
It can selectively help you quickly identify possibilities and exclude the ones that actually are impossible.
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