Scanning is one way that you can solve a Sudoku puzzle. When you first look at that puzzle you should scan it at least once and again a few times while you are trying to arrive at the solution. Take some time to analyze the puzzle as you are working it since scanning can help you to quickly pick up on a working in one or two needed numbers.
There are two basic techniques when it comes to scanning: cross-hatching and counting. You can use both of these methods alternately. You won’t be able to scan the puzzle any further when you run out of numbers to put into cells. After this you will need to start working the puzzle from a logical stand point. Some people find that it helps to mark possible numbers in the cells. You can do this using either subscripts or dots:
• Subscript marking: Use subscript to mark possible number into the cells. The one disadvantage to this is that many puzzles, such as those found in newspapers, are often too small to allow you to write in the cells. Consider making a larger copy of the puzzle so that you can read it easier or use a pencil that is very sharp so that you can write fine lines.
• Dot marking: Dot marking involves using a pattern of dots. A dot in the top left will indicate a one and dot in the bottom right will indicate a 9. The advantage of using the dot notation is that you can easily use it on the original puzzle. You will have to make sure that you don’t make a mistake with the dots or you will be led into confusion and it may not be easy to erase dots without creating more confusion.
Cross-hatching and Counting
Cross-hatching and counting are two natural methods you can use to help you solve your Sudoku puzzle.
Cross-hatching starts by scanning the rows and columns so that you can see if any particular region needs a certain number by the process of elimination. You repeat the process for every row and column. To make things even faster, scan the numbers in their order of frequency. Perform cross-hatching systematically by checking for all the digits from 1 to 9 in order.
Counting is the process of counting from 1 to 9 in row, columns, and regions so that you can tell if there are any missing numbers. Counting speeds up your solving time since you any numbers that you discover by counting are essentially “free guesses” since they don’t take a lot of analysis to discover. If you are working harder puzzles the value of one single cell can often be determined by counting in reverse. Counting in reverse is done by scanning the region, the row, and the column for numbers that can’t be right to see which numbers are left that might work.
Once you become an advanced Sukoku solver you will learn to start to look for what are called “contingencies” while you are scanning. This means that you will narrow down the location of a number within a row, column, or region to two or three cells. When each of those cells fall into the same row, or column, of the region, then you can use them to eliminate other numbers by cross-hatching and counting.
Sudoku puzzles that are really challenging might require you to try multiple contingencies. There will be times when you have to recognize these contingencies in multiple directions while at times even intersecting your number selection. A puzzle will be classified as “easy” if you can solve it by the scanning method alone. Sudoku puzzles that are more challenging won’t be solved by scanning alone but will need multiple solving strategies.
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