by Alexia Schulz

Created on: February 12, 2007   Last Updated: May 26, 2012

It's easy to get started if you want to learn to solve sudoku. The key information is that every row, every column, and every box contains the digits 1-9. No digit can appear more than once, and no digit can be missing. A good strategy for getting started is to cycle through the numbers 1-9, and find pairs in neighboring boxes. Once you find that pair, you know that the third box has to have the number in the remaining row or column. That narrows it down to 3 possible spaces for the number, and sometimes these position are already filled. What you do then is check in the other direction to see if you can eliminate any ambiguity, and if you can, mark the number down in the right space. You can often "follow" a number all around the board like this, until you find all nine of them. When you use this technique, don't forget that boxes separated by one box (top and bottom for example) count as neighboring boxes.

Another useful technique is to search each row, each column, and each box to see if you can sort out the positions of the missing numbers. One really important hint is that sudoku puzzles are full of symmetries (in fact, I find the more symmetric they are, often the harder they are to solve). While the symmetries can often be frustrating, they can also give you important clues as to where to look next for a solvable box or row. For example, if you've completed the numbers in one of the corner boxes, look to the diagonally opposite corner and often you can complete the numbers there as well. If you complete a row or column, look at the symmetric row/column on the other side of the puzzle and often you'll be able to do that one as well.

If you get stuck using the above two techniques, the next thing to try is to look for pairs of numbers appearing in neighboring boxes, using the same sort of pattern as when you went through the digits in step 1. The basic idea is that if (for example) 2 and 3 appear in column 1 in one box, and column 2 in a neighboring box, then 2 and 3 have to appear in column 3 in the remaining box. The same conclusion can be drawn if the pair of numbers is in columns 1&2 in the first box, and 2&1 in the second box.

Finally, once you get a little more advanced, you want to start thinking about which digits the blank spaces CANNOT be, in addition to which digits they can be. This is because sometimes you can fill a blank by knowing that all other blanks in the row/column/box cannot be that digit.

Happy solving!

Learn more about this author, Alexia Schulz.
Click here to send this author comments or questions.