Thus, the 8 circled in red between the two highlighted yellow cells at the bottom can be eliminated. Trying both configurations reveals that, regardless of the final answer, the number 8 cannot be a candidate in the rows connecting to the base pattern. If the two 8 connected by the dotted line are true, the other pair becomes false and vice-versa. Since these 4 cells are aligned by column and row, it is possible to apply the Sudoku X-Wing technique. In the example above, it is clear that the number 8 has only two possible solutions within the highlighted columns. Practical exampleĪccording to the basic rules of Sudoku, every row and column must contain the numbers from 1 to 9 without repetitions. Likewise, with X-Wing patterns on columns, it is impossible for the digit to be a candidate in the rows connected to the base pattern. That is, the pairs formed by the cells diagonally opposite to one another.īy testing each set of possibilities on the grid, it becomes clear that whenever the Sudoku X-Wing technique is applied to rows, the digit in analysis cannot be a candidate to any cell of the columns connected to the base cells. Since the digit has only two possible solutions in the rows or columns in analysis and each cell is directly affected by the others, the player can identify only two possible sets of solutions for the digit. The basic principle of this technique is simple. These cells must be aligned by column and row, forming a square or rectangle when connected. To be able to apply this technique, the player must find 2 rows or 2 columns where a single digit is a candidate in only two cells of each. Requirements to apply the Sudoku X-Wing strategy Together with the Swordfish, the Sudoku-X-Wing technique is also a valuable strategy for any player to learn as it branches out into more complex patterns and techniques that are required to solve impossible puzzles. It focuses on one single digit and its goal is to restrict the number of cells that can have that number as a possible candidate. It is a very straightforward technique with an easily identifiable pattern. Paul Stephans has had a long career as a technical author and it shows.Īvoid books by Carol Vorderman, she places too much emphasis on long length claims, which she may well be very good at, but she does not explain the very wide set of additional techniques that can be employed.The Sudoku X-Wing strategy is one of the most recurrent techniques that can be applied to Sudoku puzzles from a medium difficulty level onwards. It is concise, precise and also uses limited colour to draw attention to the cells featuring in a particular explanation. This is without any doubt the best book on solving Sudoku. What a shame.Ī better book, but with fewer examples, is Mastering Sudoku week by week, by Paul Stephans. However, these multiple puzzle listings are far too small to allow convenient solving since there is not enough room in the very small cell size to write all of the possible candidates. This makes this book the leader in that example class. It describes all of the advanced techniques and for each of these it lists a great number of puzzles that require that particular technique. This is a good book on how to solve Sudoku puzzles. To learn more about how and for what purposes Amazon uses personal information (such as Amazon Store order history), please visit our Privacy Notice. You can change your choices at any time by visiting Cookie Preferences, as described in the Cookie Notice. Click ‘Customise Cookies’ to decline these cookies, make more detailed choices, or learn more. Third parties use cookies for their purposes of displaying and measuring personalised ads, generating audience insights, and developing and improving products. This includes using first- and third-party cookies, which store or access standard device information such as a unique identifier. If you agree, we’ll also use cookies to complement your shopping experience across the Amazon stores as described in our Cookie Notice. We also use these cookies to understand how customers use our services (for example, by measuring site visits) so we can make improvements. We use cookies and similar tools that are necessary to enable you to make purchases, to enhance your shopping experiences and to provide our services, as detailed in our Cookie Notice.

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