The SuDoku grid has three main elements. There are
9 columns, 9 rows and
9 blocks.
Using the numbers 1 through 9, the 81 squares in
the sudoku grid must be filled so that every column, row and block
contains the numbers 1 through 9. No number can repeat within any
column, row or block.
Certain numbers are given and the puzzler must then fill in the
remainder in order to solve the puzzle. The amount of numbers given,
which ones, and their placement within the grid determine the
difficulty of the puzzle.
For this tutorial we’ll begin with a very easy puzzle which will
introduce you to some basic sudoku solving strategies.
Here is an easy grid to get you started.
To begin, look for a number which has a high
frequency within the puzzle
In our example, the number 8 appears five times so
we’ll begin by penciling in the rest of the 8s wherever they can
possibly go. We know that no number can repeat in any block so we
need to put 8s in blocks 2, 3, 6 and 7.
After lightly entering all possible 8s, we discover
that there is only one square in blocks 6 and 7 where we can place
an 8. (Remember! The 8 cannot appear twice in any column or row.)
Now we can safely enter the two 8s in blocks 6 and
7.
Now, identify another number with a high frequency
rate...
The number 5 also appears five times within the
puzzle so now we'll follow the same procedure for the 5s.
Once again, we have only a single square in blocks
3 and 5 where a 5 can possibly be placed.
Now we enter the number 5 in block 3 and 5.
Now, here's where it gets interesting...
Since we know that numbers cannot repeat in any
column, we can logically ascertain (now that we've entered 5s in
blocks 3 & 5) that some of the 5s we penciled in for blocks 8 & 9
are no longer possibilities. So let's remove those 5s.
And lo and behold, now we have only one possible
placement for 5 in those two blocks.
That completes the number 5 since every block now
contains a 5. So where do we go from here?
Now, we'll follow the same procedure for the 7s.
Again, we have only one possible placement for the
7 in blocks 3 and 4.
Now we can safely enter those numbers and remove
any 7s from the corresponding rows or columns.
And that leaves only one possibility for the 7 in
block 6. And it also nails down the 8 in block 3! Now, we're making
progress...
Now, we'll fill in the 7 in block 6 and the 8 in
block 3. Again, we can eliminate one of the 8s in block 2.
That leaves a single square for the 8 in block 2.
So we can enter the 8 and that completes the 8s for
this puzzle.
Now, it's time to change our solving strategy...
Up to now, our strategy has been to enter all the
possible for any number with a high frequency rate within the
puzzle. Now, we've got enough numbers entered into the grid that we
can use a different solving strategy.
Let's look at block 3. We have seven of the nine
numbers required. We are missing only the 3 and the 9. Looking at
the top row, we see that it already contains a 3 (in block 2).
Therefore, the 3 must go in the bottom left square of block 3 and
(Eureka!) the 9 in the last remaining square.
Wow! We've come along way towards solving this
puzzle.
And on further examination we see that the only
number missing in column 7 is the number 2. So we can enter it in
block 9.
Now you have the basic solving strategy for SuDoku
puzzles. Time to try solving some on your own. Here is a
selection of easy puzzles
to practice on. As your skill improves, move on to the harder
puzzles. Happy puzzling!
