Free Suduko

I am sure you are already pretty familiar with the common Sudoku puzzle, which has been highly popularized and meditated in the past few months by many magazines around the world. Well, if you are solving problems solving the puzzle, or if you are just trying to compare your method with the “official” one, just take a look at this.

As you must already know by now, the 81 tiny cells form a grid which also contains six three*three squares. Some of the tiny squares are filled in with numbers (digits from 1 to 9); these are called “givens”. Your job is to entirely complete the grid so that in each row, column or three*three square you have all the digits (each one being used only once).

The quickest and most common way to start solving the puzzle is to try and work out which numbers could be placed in each cell. So think what values you could attribute to each cell. The simple rule I told you before is actually the key of the puzzle: it reduces the number of possible values a cell can be filled in with. So, be careful and try to keep track of which possible digits you can attribute to a cell and soon enough you will be left with little or even with no choice!

First of all, draw on a sheet of paper the grid with all its givens. Try to make the cells as big as you can, because next you’ll have to write down in each cell the numbers that you could fill it with. Be careful while making each and every step. One tiny mistake and you must start all over again. You might want to use different color pens for each digit, it helps you see better if the digit may be attributed to the cell or not.

Now if you have completed each cell only with the numbers which may be in it, don’t be surprised to find out that in some cells there is only one possibility! But remember! After filling in a new number you must always take another look at the cells around it and erase it from the possibilities (when necessary, of course).

But in some Sudoku-s you might end up with a situation where you have multiple choices to make your next step. Well, if you are sure that all the steps you have done so far are flawless (you might check once again), it’s time to get a bit fiendish. This means you are facing a tricky Sudoku so the only way to deal with it is to take a risk. Try one of the possibilities. But you should use a soft, erasable pencil, because if you aren’t lucky from the first shot you will find it easier to pick up the game from where you left it than start all over again.
Finally, it’s time to check the result. Obviously, the easy way to do that is to check the sum of numbers on each row, column and three*three square: it should be 45.