The 9 is thus eliminated from the rest of these rowsĪs in the preceding example, there are two columns (B and C) where 9 can be in only two possible cells each (B3 and B9, C2 and C8).īecause B3 and C2 as well as B9 and C8 are in the same block (instead of the same row as previously), 9 can thus be excluded from the other cells of these two blocks. The purpose of this essay is to implement and study different techniques for solving Sudoku puzzles, a problem similar to graph coloring with fixed size and. In this second example of the Sushimi Finned X-Wing, the missing corner of the basic arrangement is J8, with an extra fin (on J7). Regardless, their application always demands high levels of concentration from the player as they work by deduction. There will thus be necessarily a 9 in the 2nd and 8th rows, either in B2 and H8 or B8 and H2. Very difficult Sudoku puzzles require the use of advanced logic techniques Perfect book for experienced Sudoku solvers. Advanced Sudoku strategies are used in the hardest levels of these puzzles and they can either help to reduce candidates or to find the solution for a specific cell.
9 can thus be eliminated from the other cells of these rows.įor column B, if 9 is not in B2, it is in B8 and inversely in column H. The same method applies in the case of two columns, the excluded candidates will then be on the rows.įor column B and H, the 9 is only possible on the 2nd and 8th row (blue cells). X-Wings are the start of a family of strategies with such evocative names as Sword-Fish, Jelly-Fish, Squirm-Bag and Burma. The following methods are not necessarily more difficult to understand that the above ones, but it is not easy to spot when to apply them.įor a given number, when it’s only possible in two cells of two different rows, and that the four possibilities are on two columns (and form a rectangle), then that candidate can be excluded for the other cells of the column.
#X wing sudoku how to
This quick Sudoku lesson explains how to recognize the X.
Solving methods > 4- Complex methods > 4.1 Associated pairs (X.wing) X-wing patterns appear often and can be used as a Sudoku solving strategy to eliminate candidates.
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