How to use x wing in sudoku

If you can find a row that contains the same pencil mark in exactly two spots, as well as another parallel row that mirrors it — containing the same pencil mark in only the same two spots, then you can use this information to eliminate similar pencil marks in the columns passing through those spots, how to use x wing in sudoku. Because of this, we can safely assume that either the light blue cells or the dark blue cells must be 4s. Armed with this, let's zoom out all the way and shift our focus to the columns involved here indicated with arrows below.

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 a very straightforward technique with an easily identifiable pattern. 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. 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. 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. These cells must be aligned by column and row, forming a square or rectangle when connected. The basic principle of this technique is simple.

How to use x wing in sudoku

X-Wings are fairly easy to spot, but a little harder to understand than some other techniques. Like others it relies on using positions of pencilmarks to infer enough to allow you to eliminate some other candidates. Once you've satisfied yourself that there aren't any easy methods you can apply to move forward, take a look at the candidate positions for 6, in rows 4 and 9. The trick to understanding X-Wings is to imagine what would happen if you chose just one of those positions - what would it do to the others? Imagine making the top left of those cells be the 6 - it would force the other candidate out on its row, and also force the candidate in the bottom left out too the red arrows. By exactly the same logic, a 6 in the top right cell would force the bottom left cell to be a 6. If you think about it, whichever position 6 occupies in the top row, forces the other to occupy the opposite position in the bottom row. Here's the clever bit - even though you don't know which row has the 6 at the left, and which row has the 6 at the right, you know for sure that both will be occupied. And because you know that the 6 will definitely be in both of those two column positions, you can look up and down those columns, and remove any other candidates! We can't remove any 6s from the left hand column this time, but there are two we can remove from the right hand column, and one of those leaves an 8 as a single candidate! What is new about this technique is that knowledge about two similar rows, lets you make removals from columns.

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The object of Sudoku is to fill a 9x9 grid so that each column, each row, and each of the nine 3x3 grids contain all of the digits from 1 to 9. The puzzle starts with some cells already filled in; your job is to use logic to fill in the remaining squares. No guesswork needed—just pure deductive reasoning. Whether you're a beginner or a seasoned pro, Sudoku offers endless challenges that sharpen your mind and make for a perfect brain workout. On the road to becoming a more proficient Sudoku player , learning several strategies and techniques to solve Sudoku puzzles more effectively is essential.

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How to use x wing in sudoku

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 a very straightforward technique with an easily identifiable pattern. 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.

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They can be formed by different digits or by the same digit positioned in different rows or columns. Not directly concerning the text, but shouldn't the next page after this be Swordfish rather than Single's Chains? No occurrence of the number in this case 6 can occur in the rows between A and B or C and D; 2. So any other 7 under the influence of cell A or B can be eliminated. What is new about this technique is that knowledge about two similar rows, lets you make removals from columns. Here is an example of combination 5. Nice graphics and good explanation. An X-Wing pattern occurs when two rows or two columns each contain only two cells that hold a matching candidate. Is this a common thing, or should there always be a way to solve the pussle without guessing? Sign up for more. The object of Sudoku is to fill a 9x9 grid so that each column, each row, and each of the nine 3x3 grids contain all of the digits from 1 to 9. Well, A and B are a locked pair of 7 s. Back to the list of tutorials Back to the Homepage.

This idea is completely analogous, logically, to pairs, triplets, etc. Here is the idea as an X wing : Consider any one candidate Consider any two distinct rows Let the candidate be limited to no more than two cells in each of these two rows Let this group of no more than 4 cells share exactly two columns The candidate is forbidden from all the cells in those two columns outside of those 4 cells Because of symmetry, one can exchange columns for rows in this rule.

They are locked because they are the only 7 's in rows B and F. Well, A and B are a locked pair of 7 s. Still confuses me. Here is an example of combination 5. We can therefore eliminate 3 from all other cells in those 2 rows as you can see in the picture:. Stopped using X-Wing on anything but squares and rectangles after I did www. Updated on: November 19, In the example above, it is clear that the number 8 has only two possible solutions within the highlighted columns. At this point, we do not know which pair the 4 will reside in. And because you know that the 6 will definitely be in both of those two column positions, you can look up and down those columns, and remove any other candidates! Of course, it works the other way too, if you can spot similar columns. You will need to solve naked singles, hidden singles, a naked pair 4,7 in row 7, a locked candidate 5 in column 7, and a naked triple 2,4,5 in column 1 first.