dailysudoku.com

[nataraj]

no difficulties at all.
only very basic steps, easy to see, not even box/line interactions.

wrong rating or wrong puzzle.

[nataraj]

To give us all something to do while the next true vh is being prepared, I suggest this puzzle from sudocue.net (Sept 25):

http://www.sudocue.net/olddaily.php?id=652&sol=0

After basic steps, this is where "vh" comes in:

[cgordon]

I thought I'd screwed up because I finished this without doing any clever stuff. But then I did it again - same result. Please- some one tell me I doubly screwed up - and that this is really a VH.

[Marty R.]

I must've missed something and did it the hard way; I used an XY-Wing and a Type 1 rectangle.

[Asellus]

I didn't use any coloring, but it took me 6 steps. No doubt someone can find a shorter route:

X Wing in R38 removes <4> from R2C3
Finned X Wing in R16 removes <7> from R3C5
{13} W Wing in R23 removes <3> from R2C6 & R3C8
XY Wing w/ pivot R2C2 removes <3> from R1C8
X Wing in R35 removes <7> from R1C4
XYZ Wing w/ pivot R7C1 removes <9> from R9C1

[keith]

This is the starting position.

[Asellus]

I should clarify...

My post was responding to nataraj's alternate puzzle, not to the Oct 12 VH.

[sheryl]

can anyone who thought this puzzle was easy, explain to me how to go the next step in elimination without actually using trial and error. here's where i am now. i would greatly appreciate the help. thanks.

+------------+-----------------+----------------+
| 1 6 5 | 4 8 7 | 9 3 2 |
| 38 34 348 | 9 2 5 | 7 6 1 |
| 2 7 9 | 136 16 13 | 8 5 4 |
+------------+-----------------+----------------+
| 78 39 678 | 2 67 349 | 349 1 5 |
| 5 2 367 | 136 1467 1349 | 349 8 3679 |
| 4 1 367 | 36 5 8 | 239 239 23678 |
+------------+-----------------+----------------+
| 39 5 234 | 8 14 124 | 6 7 139 |
| 6 8 1 | 7 9 2 | 5 4 3 |
| 79 49 247 | 5 3 6 | 1 249 8 |
+------------+-----------------+----------------+

[Marty R.]

Sheryl, a next step could be an XY-Wing of 49-39-34, with the Wing being pivoted in r9c2.

[sheryl]

Marty, isn't this still guessing. one still has to say, if the 49 is a 9 then the 39 is a 3 and the 34 is a 4 but in reality the 49 is 4 and the 39 is a 9 and the 34 is a 3 so you still have to go thru all the machinations to find the answer and if you pick the wrong "pivot" then you end up in a hole and have to repeat that. what i want to understand is how you elimate the possibilies, how do you Pivot the 49 into a 4 and not the 9.

[kragzy]

I'm with nataraj and cgordon on this one. I've done the puzzle twice - both times with easy straightforward moves - 12 minutes first time, 11 minutes for the second. I deliberately tried to attack the puzzle from a different direction the second time.

I'm not trying to be smart because there are many people on this forum who live in a Sudoku world way above mine, but I am puzzled as to how this puzzle could develop into a VH.

Cheers

[Asellus]

Sheryl,

Let's make certain you are viewing the XY Wing correctly:

[kragzy]

I appreciate you're just trying to help Sheryl on XY wings, but if this is the point where others have started to use advance techniques in this puzzle, my question is Why? There is only one 9 in Box 4. The puzzle falls apart from this point.

[Asellus]

Sheryl,

Your grid has lots of candidates that can be removed. For example, look at <2> in Box 8, or at <3> and <8> in Column 9, or <4> in Box 9. It is important to be careful about removing candidates from "buddie" cells when you solve a cell. I suspect you'll find that that XY Wing isn't even required.

[keith]

[kragzy]

Keith,

wrong
wrong
right
wrong
wrong
wrong
right

Check the cells that re already solved.

Cheers

[duffy]

Keith,
I hope Sheryl doesn't get a headache from your statements that are true if you ignore all the singles, but otherwise are mostly not true! But I think your point must be that her grid (which is the same as the easier-to-read one posted by Marty) does allow for these statements on the basis of inspecting the unresolved candidates only.

Sheryl,
My suggestion would be to clean up the extra candidates based on the singles and note the 34 locked pair in r4, as a next step. And maybe an aspirin!

Don D.

[duffy]

Sheryl,
Considering Marty's suggestion and your response, I think you don't have a handle on xy-wings yet. The wing he noted eliminates the 3 in r2c1. Maybe think of that 3's effect if it were true: it would make r2c2 a 4, and make r7c1 a 9: these would then leave r9c2 with no remaining candidate.

Don D.

[sheryl]

well, everyone, thanks for trying. here's where i am...
keith, i think you have the wrong day's puzzle. i say this because of your first statement which says that r6c9 is the only cell that can be an 8. in fact 8 is given in that box in r5 c8.

kragzy and asellus, i see your points. i did not notice the 9 in box 4 nor the 2 in box 9 so i have to be much more careful in the future. that probably would have helped alot. also, asellus, your explanation of the xy wing was very helpful as in fact i did not have the xy wing correct. and now i see how that deduction was made.

the only thing i now question is how does one figure out the xy wings. what is it i am to look for. i have read several pages on xy wings and it is quite confusing to me on how to identify them in an actual puzzle so any tips would be most welcome

duffy, i am going to take your suggestion and clean up the 'candidates' and see how that plays out. then i will take the aspirin.

i might be back again tomorrow with more questions. i hope you folks don't mind because this has been extremely helpful to me. i am determined to 'get to the bottom' of solving the VH sudokus.

thanks again!!!

[keith]

(revised Oct 23, 2007)

My solver was thrown off by having incorrect candidates in the unsolved cells.

Here are the correct candidates: