SOLVING SUDOKUS

All these Sudoku puzzles are solvable using logic and reason alone. You don't need any understanding of Maths, that's probably what makes them such a popular puzzle!

There is only ONE single solution to any puzzle generated by the program.
If you make an obvious mistake, like putting two of the same number in a line, the program will warn you.
Here are some hints and tips to get you started:

In every row, column and box, ALL the numbers 1-9 are used only once. Look at this finished puzzle and see for yourself. (See Fig 1)

Fig 1. The numbers 1-9 are used only once in each row, column or box

Don’t guess. If you guess wrong then you’ll get yourself in trouble in no time.

When you turn ‘Hints On’, the computer will automatically fill in all the possibilities for each square. On paper you can do this yourself by filling in the entire puzzle with tiny numbers and crossing out any number that are already used in the corresponding row, column and box. Although this can take quite a bit of time it’s the best way to solve a puzzle. But luckily the computer does this for you in this version!

Here’s what to look out for with those tiny numbers:
If you see any squares with only one number then you can fill this number in immediately. (See Fig 2)

Fig 2. In this example you can put 8 into the middle square as the hints say that it's the only entry possible.

The little hint numbers will automatically update every time you place a new number.

Check every single row, column and box and….

1. If you see a number that’s suggested by the hints only once then you can fill that one in, even if it's not the only number in it's square. (See Fig 3)

Fig 3. Look at the last square in this box, the number 6 is suggested here but it's not mentioned anywhere else in the box, so you can fill it in as there's nowhere else for it to go.

2. If only two different numbers are used in two squares then you can correctly assume that these number don’t go anywhere else but those two squares. (See Fig 4)

Fig 4. In the 4th and 6th squares in this box the numbers 2 and 5 are used, now as a '2' must go into one of these squares and a '5' into the other then logically you can asume the the first square DOESN'T contain a 2. So in this example you can fill in a 3. Similarly the third square must be the number 7.

3. Following on this point; if only 3 different numbers are used in any three squares (in a single row, a single column or in a box) then you can correctly assume these numbers don’t go anywhere else. (See Fig 5)

Fig 5. In the 4th, 5th and 6th squares in this box the numbers 7, 6 and 1 are used, now as a '7' must go into one of these squares and a '7' into another and a '1' in the last then logically you can asume the the third square DOESN'T contain a 1 or a 6. So in this example you can fill in a 5. This is the hardest point to grasp but if you can understand it then you're on you way to solving the hardest Sudoku puzzles.

Don't worry if you can't understand all these points at first read. Playing through even a couple of Sudokus slowly will make these hints more clear. And perhaps you'll see what all the fuss it about :)