Sudoku Hints and Tips

Welcome to the Hints and Tips section of The Puzzle Club. Here we look at strategies you can use to help you solve our Sudoku puzzles.

The most simple tactic and the one that can be used to solve a large number of puzzles eventually is through basic elimination.

With this technique you simply go through the puzzle and cross reference the numbers that are already placed in the grid, to find where a number must be placed in a row. Here is an example of this technique in action:

Let's use this technique to see if we can place any '1's in this section of a puzzle. The first thing we note is that the first and second row already have a '1' in them.

Now, we know that a number can only appear once in a row. Therefore we can place the '1' in the third row straight away: it must be in cell 7. It cannot be in the other empty cells in that 3 x 3 square because placing it anywhere would break the rule that a number can only occur once per row. Therefore we place the one:

This technique can be used throughout most puzzles, and will help you to deduce a good deal of numbers, if not all. Remember when a number is placed to then go back through and see if further deductions can be made as a result - and they usually can.

Use Pencil Marks

If you like, you can try and hold all the possible values for a cell in your head. However this soon becomes very hard indeed. Therefore when you have reduced the possible values for a cell for instance to two or three, you might like to write them in the cell in smaller numbers, ready to cross out as you advance in the puzzle.

For instance, look at the example we just placed a '1' in again:

Imagine you want to work out what the two squares at the end of the first row are. Using the elimination technique above, you know that these cells cannot contain any of: 1,2,3,4,7,8,9, because these are already contained in the 3 x 3 square and row these cells belong to. We therefore know that they must contain 5 or 6 even though we're not sure which way round. Therefore write these in small letters in those two cells.