Sudoku Strategy Y Wing

Most techniques tips tricks about how to solve sudoku puzzles stop before they generalize ideas.

Sudoku strategy y wing. As a last resort for solving really difficult puzzles when you have tried everything else the hook. From the start i have found a superb tough sudoku puzzle with a sequence of five y wings and this illustrates the full range of this strategy. You can use y wing if each of the two candidates in the pivot forms a conjugate pair in two. The cell in the center is called the pivot.

This is an excellent candidate eliminator and is also known as xy wing. The red square in the above image is the pivot. Load example or. This is a tad specific for my taste.

One of the more complex sudoku strategies is the x wing and its cousin the swordfish. Sudoku dragon daily online help manual introduction sudoku history strategy advanced theory guessing symmetry variants guides guessing symmetry hook or x y wing sudoku puzzle solving guide step. Y wing example 1. Y wing starts with a square that contains exactly two candidates.

This square is sometimes called a pivot or hinge. Probably best just to show you. An xy wing is a solving technique that uses a short chain of 3 cells. The forth corner is where the candidate can be removed but it leads us to much more as we ll see in a minute.

X wing extends to swordfish and jellyfish while y wing brings a nice set of other rules which we will examine in later articles. These rules are useful for solving the really difficult sudoku puzzles when all else has been tried and failed. Below is an example of an xy wing. We take a look at this extremely powerful and important technique which comes up again and again in difficult puzzles.

Xy wing involves 3 different cells each with exactly two candidates pencil marks that are related to each other in such a way that you can make some logical conclusions. The name derives from the fact that it looks like an x wing but with three corners not four. Note how the 3 cells form a y see the red lines it s really more like a v. The first three are pictured here but you can load the puzzle into the solver to see the remaining examples.

Although y wing and x wing have similar names the methods are different. Y wing is a strategy that allows you to eliminate candidates. In looking for twins and permutations we restricted ourselves to looking at possibilities within a single group. When to use y wing.

Let s look at figure 19 1 for the theory. A y wing considers strength in cells to deduce strength in candidate location.