Sudoku puzzles are a type of Latin Square  any character cannot appear more
than once in each row or column, with an extra constraint that that character also cannot
appear more than once in each 3x3 cell area. In total, there are 27 such domains in a
regular Sudoku puzzle. The puzzles that you find almost everywhere, including in the
Soduku section of this site have numbers, although there is a version of each day's puzzle
that has alternative numbers in it so that you do not have a sign that you can readily
recognise unless you can read Gurmukhi numbers.
In this section, there are some fun variants of the regular Sudoku puzzle  the 'normal'
puzzle being the 'Wordoku' which uses a nineletter word instead of numbers. Where letters
are used instead of numbers, the letters are displayed next to the puzzle.
All of the other puzzles, such as the one on the right, use more than the 27 domains (nine
columns, nine rows and 9 3x3 squares of the regular Sudoku, they have one or four extra
domains. The additional domains work in the same way as the usual 27 insofar as they have
all nine characters in them and they cannot have any of them appearing more than once.
The puzzles with one extra domain in are easy to differentiate from those with four
extra domains in because there are only nine coloured cells in total whereas those with
four extra domains have each domain in contiguous blocks; so, for example, the Motifdoku
puzzle has four distinct, joinedup coloured areas so there is no confusion.
So, how do these extra domains work?
On the right, you can see one of the Day Of the Week puzzles 'DOWdoku'. This is for
Thursday so there is a lowercase 't' in only nine picture elements.
The regular 27 domains work as normal but there is the 28^{th} domain in the
form of the 't'. This extends across five of the 3x3 domains as well as four columns and
five rows. In the example on the right, you can see that the three in the topright 3x3
domain stops there being a three in the middle column of the bottomright 3x3 domain.
This would normally leave open the possibility of the three for that domain being undefined
and therefore able to go in either of the two cell marked with the red rectangle.
However, the three in the middle cell is in the 't' which extends into the upper half
of the red rectangle therefore meaning that the only cell that three can go in is the
lower of the two.
In this example, the three has been written in and therefore the seven ash also been written
in by a process of elimination.
Without that extra domain, there would be no way of deducing where the seven in the middle
3x3 domain goes. However, whilst the seven in the 3x3 on the right eliminates the middle row,
leaving the cells highlighted with the blue rectangles, there is a seven on the bottomright
of the 't' that means that a seven cannot go in the 't' anywhere else. In this way, we can
deduce that the only cell a seven will go in is the bottomleft cell.
This is what the puzzle looks like when it is finished. As you can see, as much of it was
done just by inserting numbers but after a while, I resorted to using dots  see the
tutorials for Kakuro and Quadrata puzzles in case you haven't come across them yet.
This is what a Sudoku with an extra four domains looks like. Each additional domain is a
contiguous block, that is to say that there are no odd cells separated from any block as
there are in the single extra domain puzzles.
Click on the puzzle to animate it so illustrate where the 31 domains are.
Each 3x3 additional domain is marked as a grey area and has the same rules as the
additional domain in the other puzzles.
Click here to stop the animation.
This is the puzzle completed. Again, you can see that I used the spot method to complete it.
You don't have to use spots if you are the sort of person who can memorise all of the data,
it is just that it is sometimes a lot more convenient to use them.
Here, like in the Quadrata tutorial, I have marked the letters with numbers and used those
to solve the puzzle where dots are required.
Finally, you can use the solutions from the archive to check the answers to the puzzles.
Have Fun.
