The New Sudoku Players' Forum

[Aniedunai]

Hello guys,

So, as mentioned in the title, I'm stuck on this particular level of sudoku. I've been to a sudoku solver and it tells me to use the X-wing strategy on r2c2/r2c8/r9c2/r9c8 for the number 2.
While this doesn't necessarily give any solution for single candidates, I'm trying to understand why specifically the r2c8 number 2 and not the other twos in r2c7/r2c9 or the twos below on r9c7/r9c9.

Thanks for the help

Code: Select all


458  4589 589  | 2  7    3 | 568  468  1
6    253  1    | 8  4    9 | 2357 27   237
2348 7    38   | 16 16   5 | 238  9    2348
------+-------+-------------------------------
138  389  4    | 36 3689 7 | 1238 5    2368
3578 358  2    | 4  368  1 | 9    78   3678
1378 6    3789 | 5  389  2 | 4    178  378
------+-------+-------------------------------
28   1    68   | 7  5    4 | 268  3    9
347  34   367  | 9  2    8 | 5    167  1467
9    2458 578  | 13 13   6 | 278  2478 2478





[champagne]

In the columns c2,c8 you have only 2 ways to put the digit 2

r2c2=2 r9c8=2
r2c8=2 r9c2=2

In both cases, the 2 is defined in r2 and r9. It can not be in the other cells in r2 and r9.

This is the simplest cases of such patterns.

[Aniedunai]

Yes, I see that now. Since there's only two places the twos can go in those two columns we can then apply the X-wing method.
You're saying that if there were to be a third number two in any of those two columns the method would be invalid?
I really gotta do some X-wing based sudokus if this is the most basic one.

Thanks for the response

[champagne]

The basis for this "fish" pattern has relatively simple requirements

X-wing

a digit locked in two columns for 2 rows
a digit locked in 2 rows for 2 columns (like here)

swordfish

a digit locked in 3 columns for3 rows
a digit locked in 3 rows for 3 columns

... can continue with 4,5

and many possible variants sightly harder to catch

[m_b_metcalf]

I really gotta do some X-wing based sudokus if this is the most basic one.

If you look here, for puzzles rated 3.2/x/y, you'll find hundreds of such puzzles (in line format).

Regards,
Mike

[Aniedunai]

Thanks a lot for the responses and suggestions. I'll look into those puzzles for more practice.

[champagne]

Thanks a lot for the responses and suggestions. I'll look into those puzzles for more practice.

If you follow mike's proposal, the Xwing is the hardest step, you should solve all such puzzles.