Video:Sudoku Tips and Strategywith Daniel Sanz
Learn more about squeezing, cross hatching and reducing, which are three basic tips to help solve a Sudoku puzzle.See Transcript
Transcript:Sudoku Tips and StrategyHello I’m Daniel Sanz with About.com and today I’m going to teach you some tips and strategies for completing a Sudoku puzzle. There are many, many ways to solve a Sudoku puzzle however these three techniques are very effective at helping you get started.
Squeezing to Solve Sudoku
The first basic technique is called squeezing. Squeezing is the process of using two solved numbers in connected blocks to solve the same number in the last block. In the graphic you can see that the number 2 has already been solved in the A and B blocks. The rule states that each row must contain each digit only once. In this case, the B block 2 has already been solved and sits in the top row. Therefore there cannot be another 2 in the entire row. The same holds true with the bottom row, therefore leaving only three middle squares in the C block with the option of containing the 2. We can see that the 5 and 8 have already been filled in and that narrows down only one possible location for the 2. And that's how we use this information to fill in the remaining block.
Cross Hatching to Solve Sudoku
The next technique is called cross hatching. In cross hatching you use the technique of cross referencing other available rows and columns to further eliminate possibilities. In this example we can see that the 7 has already been filled in for the A and B block. This eliminates the first and second column leaving only the third column open. However you can see there is a space above and below the 3. In which of these boxes do we put the 7? If we were to put the 7 in the top box we could cross reference it with the rest of the row. We see there is already a 7 which means we cannot have a second one in this row. That eliminates the top box as a possibility leaving only the bottom one as an option for the 7.
Reducing to Solve Sudoku
This next technique is called reducing. Reducing begins when you have three or fewer open spaces in a 3 by 3 sub-region. As the rules state you have to have the numbers 1-9 in each sub-region so here we have to make note of which numbers are missing. In this case, the 3, 4 and 7 are missing so we pencil them in small in each box. The process of reducing combines squeezing and cross hatching to determine which one of those numbers goes to which box. In this case we can see this available box; we cross reference it with the horizontal row and we can find that the 4 has already been used. This eliminates 4 as a possibility. Doing the same thing for the vertical column, we see that the 3 has already been used therefore eliminating the 3. This leaves the 7 as the only possible answer for this box. You want to go to each sub-region and continue to do this until you fill in as many of the boxes as possible.
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