Solving Sudoku – The Basic Methods

Do you want to learn how to solve Sudoku puzzles but don’t know where to start? Read on! In this missive, I discuss the basic solving technique.

To start, consider the following puzzle:

Look at the cell marked in blue. An experienced player should be able to look at the puzzle and immediately know what the solution is for that cell. Scan the puzzle above that cell and also to the left. Consider that the value 1 cannot occur in any of the empty cells marked in green. We see that the blue cell is the only cell in the lower-left 3×3 group where the value 1 is possible.

(The keen observer will see another opportunity elsewhere in the puzzle where a 1 must be the solution for a cell.)

While solving a puzzle, as you’re entering values or eliminating possibilities, constantly look for these opportunities since these are the easiest to find.

Okay, so you applied this technique as much as you can and you’re stuck. What next? Consider the following diagram of the above puzzle but with a few values filled in:

Although we can still apply the first technique, let’s see if we can apply the second basic technique. Consider the cell marked in blue. That cell belongs to three groups: a column, a row, and a 3×3 square. Note that the value of the blue cell cannot be the same as any other value in those three groups. So, for that cell, list out its possible values. We see that eight possible values can be eliminated, leaving only one possible value for the cell: 1.

To find opportunities to apply this technique, look for groups with lots of values already filled in.

I’ll leave the rest of the puzzle to you. Click here to print out a clean copy of this puzzle. It’s the first puzzle in that document.

Using these two techniques, you can solve most puzzles published in newspapers and magazines. To practice, try out the Beginner Puzzles. In my opinion, the best way to solve Sudoku puzzles is by pen and paper, relaxing in an easy chair.

When starting out, it may be useful to write in the possible values in small print at the top of a cell, crossing them out as you progress through the puzzle. But with experience, you should be able to apply both of these techniques without making any notes.

In later columns, I’ll cover the more advanced solving techniques. Next up, single-group partitioning.

Hans

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