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The Object of SuDoku
Each SuDoku is made of 81 cells, divided into
9 rows, 9 columns, and 9 boxes. The
boxes are 3 cells by 3 cells, and are marked off by the
thicker lines. An example is shown just below. Notice that
some of the cells contain a digit, 1 through 9. The object
is to fill in the empty cells so that the digits 1 through 9
appear:
• exactly once in each row
• exactly once in each column
• exactly once in each 3 x 3 box
That is all there is to it. Sounds simple,
right? Here’s a sample
puzzle for you to try:
Tactics for solving SuDoku
Look for places where there is only one
number possible fo r
a cell. How can you tell? Here is an example. Consider the
following (partial) puzzle:
The red cell has to be a "4". Why? There
are several ways to think of it. Consider the 4s which are
already showing -- each eliminates the possibility of
another 4 in a particular row, column, and box.
So there is only that one cell left in
that box in which a 4 is possible. Since the rightmost box
must have a 4 in it somewhere, the one possible cell is
where it goes.
The reasoning can be more complicated than
that. Consider this example:
For the middle box, we do not know exactly
where the 4 is, but we know it must be in one of the two red
cells. That means the third row is "spoken for" and we can
remove it from consideration, leaving just the one cell in
the rightmost box.
Believe it or not, there are even more
convoluted lines of reasoning that can come into play, but
this much will let you get started on any
SuDoku
puzzle.
More SuDoku Strategy
Generally speaking, the more information
you have, the easier it is to fill in the remaining
unknowns. So look for places where you have a lot of
information.
Does one box have 5 cells filled in, where
the others have at most 3? Start there. Does one row have 6
cells filled in, where the others have at most 4? Start
there. Does one column have 8 cells filled in? You know what
the last one must be!
One less obvious example of this -- count
how many of each digit you have. If you have a lot of "5",
the remaining 5's should be comparatively easy to find.
Final Thoughts
Like anything, solving SuDoku puzzles gets
easier with practice, so keep at it! One thing to keep in
mind, though: with SuDoku, if you find that you have made a
mistake somewhere (for instance, if you have 2 “3”s in the
same box), it is generally easiest to start over entirely.
Be sure of each step before you take it! Once you start
guessing, the puzzle is likely to fall apart. Finally,
always remember: it is just a puzzle.
SuDoku is meant to be enjoyed. So make sure to
have fun!
Oh, and here’s the solution to the sample
puzzle. Hope you didn’t peek!
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