Solved up until here, I took the sudoku through an online solver and it seemed to use a guess and check strategy? Is that the only way of getting the solution or am I missing something?


2 Answers 2


By simple elimination of candidates, you can show that these four cells can only be 2 or 8: (6,3) (6,5) (7,1) (7,5)

Now look at two of these cells: (6,3) and (7,1). Because of the way the four cells above are connected, if one of these is 2, the other must be 8, and vice versa. Therefore, cells (8,3) and (9,3), which are connected to both of these cells, cannot be 2 or 8. From that and the rest of the numbers in column 3, cells (8,3) and (9,3) must therefore be a 57 57 pair.

Now cell (8,2) must not be 5 or 7, so it must be a 6.

  • $\begingroup$ Cheers! Makes sense now. Never had to solve using logic like that before.. $\endgroup$
    – jhwz
    Dec 26, 2019 at 9:23

In the middle block, the base-middle cell is either $2$ or $8$, and the cell below is then $8$ or $2$, with the left-most cell on that row $2$ or $8$ again. Either way, the top-right cell of the left-middle block is either $2$ or $8$ (also due to the top-left block), and so cannot be a $5$, and also now the $5$ has only one place to go.


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