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Sudoku Algorithms

Y-Wing
The Y-Wing Sudoku pattern is reminiscent of the X-Wing pattern, as it also consists of four interrelated cells.
Y Wing Example An example of the Y-Wing pattern is shown in the picture on the left. The Y-Wing is formed by four cells: B3, B6, G3, and G6, with possible values of '1', '2', and '3' marked yellow. If cell B3 has a value of 1, then cell G3 must have a value of 2. If cell B3 has a value of 3, then cell B6 must have a value of 2. This means that, in any scenario, the number 2 should be in either cell G3 or G6. However, the number 2 cannot be in cell G6 since it is connected to both cells G3 and B6. Therefore, we can remove the hint of '2' marked red from cell G6.

Unlike the X-Wing pattern, the four cells in a Y-Wing pattern do not necessarily form a rectangle.
Y Wing Example In the next example, the Y-Wing cells are A4, A8, B6, and B7. If cell A8 has a value of 2, then cell A4 must have a value of 7, and 7 cannot be in cell B4. Conversely, if cell A8 has a value of 3, then cell B7 must have a value of 7, and 7 cannot be in cell B4 either. Therefore, we can remove the hint of '7' marked red from cell B4.