The New Sudoku Players' Forum

[EnderGT]

This puzzle is rated as Tough. I can frequently solve puzzles by this publisher at this level of difficulty completely without pencil marks, and only rarely have I had to use something as advanced as an X-wing or XY-wing to solve them. But this one has me completely stumped. Maybe you guys can show me what I'm missing?

The original:

Code: Select all

. . . | . . . | . . 5
. 1 . | . 4 5 | 7 . .
. 3 . | . 1 . | . . 8
------+-------+------
6 . . | . . 9 | . 8 .
. . . | 5 . 7 | . . .
. 8 . | 1 . . | . . 2
------+-------+------
4 . . | . 7 . | . 6 .
. . 7 | 8 5 . | . 3 .
9 . . | . . . | . . .


And my stuck state: Edit: advanced by applying the hidden pair pointed out by Pat (thanks!) and the XY-wing pointed out by Glyn (thanks!).

Code: Select all

27      47      246     | 2367    9       8       | 1346    124     5
8       1       269     | 236     4       5       | 7       29      369
257     3       24569   | 267     1       26      | 469     249     8
------------------------+-------------------------+---------------------
6       47      15      | 24      23      9       | 15      8       34
23      9       124     | 5       8       7       | 1346    14      346
357     8       45      | 1       36      346     | 9       7       2
------------------------+-------------------------+---------------------
4       5       38      | 9       7       23      | 28      6       1
1       26      7       | 8       5       46      | 24      3       9
9       26      38      | 246     236     1       | 248     5       47


Thanks in advance.

[Pat]

in c8,
"hidden" duo {5,7}

[Glyn]

Next move is one you have done before. There's an XY-Wing on r6c3 which removes a 7.

There are some locked candidates as well, but with the wing you won't need them at all.

[EnderGT]

Next move is one you have done before. There's an XY-Wing on r6c3 which removes a 7.

Yep, found that right as you were posting

Edit: And, as you said, that solved the puzzle. Thanks to all!

[udosuk]

EnderGT glad you received your help but why did you edit out all the previous pencilmark states? Because of that we late-comers can't easily understand about the moves pointed out by the experts who helped you. (It can be done by redoing the whole puzzle from scratch and guessing which state you got stuck in, but too time consuming.)

At the moment your current "stuck state" can be solved by singles and hidden pairs, not much worthy (compared to its previous state with the xy-wing) to be shown there.

IMHO you should have just appended the new stuck states below all the previous ones instead of overwriting them. Just putting in my 2 cents worth.

[EnderGT]

EnderGT glad you received your help but why did you edit out all the previous pencilmark states? Because of that we late-comers can't easily understand about the moves pointed out by the experts who helped you. (It can be done by redoing the whole puzzle from scratch and guessing which state you got stuck in, but too time consuming.)

At the moment your current "stuck state" can be solved by singles and hidden pairs, not much worthy (compared to its previous state with the xy-wing) to be shown there.

IMHO you should have just appended the new stuck states below all the previous ones instead of overwriting them. Just putting in my 2 cents worth.

That thought occurred to me, but only after I had left for the day. In the future, I'll leave the pencil marks alone

[udosuk]

In the future, I'll leave the pencil marks alone

Okay.

[Pat]

EnderGT glad you received your help but why did you edit out all the previous pencilmark states? Because of that we late-comers can't easily understand about the moves pointed out by the experts who helped you.

At the moment your current "stuck state" can be solved by singles and hidden pairs, not much worthy (compared to its previous state with the xy-wing) to be shown there.

yes! thanks udosuk for this comment.

( i now regret not having quoted the original post inside my own response -- you would've seen it was too early for me to even mention the eventual XY-wing -- at that point EnderGT couldn't have seen any XY-wing as he had not yet gotten the duo in c8--- )

[Carcul]

[r5c3]=2=[r5c1]=3=[r6c1]=7=[r6c8]=5=[r4c7]=1=[r4c3]-1-[r5c3], => r5c3<>1 and the puzzle is solved.