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Sudoku Notes
Classic
Sudoku
The rules for solving classic sudoku puzzles are very simple. Using the
numbers provided, you have to fill the grid in such a way that each row,
column and 3x3 region contains the digits 1-9. The process is based entirely
on logic - there is no arithmetic involved, no guesswork, and each puzzle
has a single solution*.
Sudoku-X
This adds an extra dimension to the sudoku puzzle challenge. As well as the
rows, columns and regions, each of the two main diagonals (highlighted in
yellow) must contain the digits 1-9. The solving process is the same as for
plain sudoku.
Samurai
Sudoku
Ostensibly five plain sudokus - interlinked to form an "X" shape. Each
corner region of the central puzzle overlaps another sudoku and creates
interplay. Thus Samurai Sudoku should not be regarded as five separate
puzzles, but as a whole.
Samurai
Sudoku-X
Not for the faint-hearted. Combining the challenge of Sudoku-X and the
overlapping interplay of Samurai Sudoku, even the easy Samurai Sudoku-X
puzzles demand a keen eye.
Killer
Sudoku
The same rules apply as for classic sudoku - every row, column and 3x3
region must contain the digits 1-9 - but instead of having clue numbers to
start you off, the Killer Sudoku grid is divided into coloured segments. The
numbers placed in these must add up to the number printed in the top left
corner. Within each coloured area, no digit may be repeated.
Most
publications which feature Killer Sudoku use areas contained within dotted
line borders, rather than colours. The software we use to design puzzles does
not, unfortunately, allow export of grid artworks. We can only take screen
grabs and the legibility of some numbers suffers as a result. If anyone is
aware of (preferably free) software which allows export of grids we'd like
to hear from you. Please note, such software MUST allow puzzle design - we
don't want a generator. If you know of anything we might find useful please
EMAIL.
DIFFICULTY LEVELS
Our Sudoku puzzles have five difficulty settings.
Junior puzzles use only one principle of
logic for completion, namely that there is only one square in which a
particular digit can be placed.
Easy puzzles take it one stage further,
requiring the solver to identify the only candidate which can appear in a
particular square. This is the simplest form of candidate elimination.
Medium and hard
puzzles introduce further processes of (usually) linear elimination. This
generally means removing candidates from particular squares because they
must appear in a choice of squares elsewhere. Sometimes several eliminations
are needed before a particular square is left with just one possible
candidate.
Extreme puzzles demand extended logic
based on conjugate relationships within "shapes" formed by
particular candidates. These shapes have been given many - often exotic - names,
such as X-Wing, Swordfish, Skyscraper and the delightfully named Squirmbag.
Essentially the logic involved is quite simple. The difficult part is
spotting candidates which form these shapes.
Why are
Sudoku-X, Samurai, Samurai Sudoku-X and Killer available as print-only?
We use
Crossword Compiler to produce interactive puzzles. As yet this
software does not support these sudoku variants. While it is possible to
generate html versions, they behave as crosswords not sudoku puzzles.
Additionally, since these variants are generally more complicated it is
often better to print them anyway so that you can pencil in candidates.
Software limitations mean it takes longer to turn these variant sudoku
puzzles into printable artworks, so updates are generally less frequent than
for classic sudoku. The grid sizes for Samurai and Samurai-X puzzles are
generous, both to retain clarity and to make it easier to pencil in
candidates. You may need to reduce sizes before printing.
* There has been recent
discussion on internet forums about "uniqueness". If a puzzle is
described as having a unique solution, that does not necessarily mean it has
only a single solution - rather (and this is not a case of linguistic
pedantry) it could mean there is only one unique solution. By logical
extension that means there may be other solutions which are not unique. Each
sudoku we design for UKPuzzle has a single solution
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