Sudoku Strategy - Scanning

I'm going to share with you a foundational sudoku strategy....one that will shave minutes (if not hours) off your solving time. The technique is really simple and once you understand it, your solving ability will grow drastically.

The strategy I am talking about is called scanning.

What is scanning?

Using the rules of sudoku as a guide, we know that every row in our puzzle will contain the numbers from 1 to 9. There will be no duplicates and no missing numbers. Knowing this, we realize that every big row (the three rows contained in each block), will have every number from 1 to 9 three times. This is what I mean:

This is true for every big column as well, as demonstrated below:

With this idea in mind, whenever you find a big row (or big column) that has a given number twice, you can narrow down the possible boxes where the third number can be. This is known as scanning. Here's two examples:

Using scanning to solve your sudoku puzzle: A real-world example.

This is how you might use scanning when solving your own sudoku puzzles. Look at figure 5:

Study this puzzle closely. Pay particular attention to the colored ovals I've added.

Red Oval

Using the scanning strategy, we know that there must be an 8 somewhere in this section. The only problem is we have no way of being certain at this stage. Using the show itself technique, we would write in 8's in each of these boxes, and erase 8 as a possible answer from the other boxes.

Green Oval

We are closer to an answered box in this section as the puzzle maker has given us a 9 as a clue. This leaves only two possible boxes for a 1 to fit into, as circled in the example.

Blue Oval

This is a perfect example of how scanning can help you solve sudoku puzzles much faster. As you can see, there are two clues given in this section, 8 and 6. Using scanning, we know that there must be a 1 in the remaining box. You are now one box closer to solving this puzzle.

Well, I hope this article on using the scanning strategy to solve your sudoku puzzles was helpful. If there are parts you find vague, write in a comment to this post and I'll do my best clarify. This is just one sudoku strategy; I plan on posting in the near future, so check back often.

Happy Solving!