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Jan 28 VH
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keith



Joined: 19 Sep 2005
Posts: 3313
Location: near Detroit, Michigan, USA

PostPosted: Mon Jan 28, 2008 4:11 am    Post subject: Jan 28 VH Reply with quote

This may be the toughest "Very Hard" puzzle ever!

Keith
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Marty R.



Joined: 12 Feb 2006
Posts: 5728
Location: Rochester, NY, USA

PostPosted: Mon Jan 28, 2008 6:04 am    Post subject: Re: Jan 28 VH Reply with quote

keith wrote:
This may be the toughest "Very Hard" puzzle ever!

Keith

No argument there. Very few freebies at the start and much more than the usual number of polyvalue cells. I must've missed some moves, since I used techniques that aren't required for these. But it took me:

ER
Finned X-Wing
X-Wing
Type 1 UR
XY-Wing
XY-Wing

There were a couple of potential W-Wings, but I couldn't see any connecting strong links.

Definitely a VH VH.
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nataraj



Joined: 03 Aug 2007
Posts: 1047
Location: near Vienna, Austria

PostPosted: Mon Jan 28, 2008 7:23 am    Post subject: Reply with quote

Very tough, indeed!

coloring on 7 removedd 7 from r6c5 (don't know if that helped any)
xwing 8 that was the breaktrough (r69 c58)
but not done!
xy wing 57-78-58 removed 5 from r9c1
opens up another xy wing 15-14-45 removes 5 from r1c3

that's it.

There was another coloring on 7 removed 7 from r2c2 and r5c5 but I don't remember exactly when (before or after the xy wings?) or whether it was necessary or not.

Great puzzle
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storm_norm



Joined: 18 Oct 2007
Posts: 1741

PostPosted: Mon Jan 28, 2008 9:08 am    Post subject: Reply with quote

there is one elimination on 7 via coloring before the x-wing on 8.

after the x-wing on 8, get rid of some box eliminations and a naked pair {5,7}



Code:
2       1357    56      | 156     167     8       | 4       136     9
147     179     46      | 2       3       179     | 5       16      8
15      1359    8       | 1456    1469    159     | 2       136     7
---------------------------------------------------------------------
9       57      1       | 38      57      6       | 38      2       4
8       6       2       | 134     147     17      | 37      9       5
57      4       3       | 9       58      2       | 6       78      1
---------------------------------------------------------------------
3       58      7       | 568     69      59      | 1       4       2
6       158     9       | 158     2       4       | 78      57      3
145     2       45      | 7       18      3       | 9       58      6


this grid is after the x-wing on 8 and after the box eliminations, the x-wing on 7 is in r14c25

but that doesn't solve it, its the aforementioned {578} and {145} xy-wings that kill it.


Last edited by storm_norm on Mon Jan 28, 2008 9:30 am; edited 3 times in total
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andras



Joined: 31 Oct 2007
Posts: 56
Location: Mid Wales

PostPosted: Mon Jan 28, 2008 9:24 am    Post subject: Reply with quote

Hmm, I thought it was pretty straightforward, although it did keep going a bit!

An x-wing on 8, as already noted.
An xy on 5,7,8
And another xy on 1,4,5.

QED!

John
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Earl



Joined: 30 May 2007
Posts: 587
Location: Victoria, KS

PostPosted: Mon Jan 28, 2008 2:31 pm    Post subject: Jan 28 VH Reply with quote

Lots of x-wings, xy-wings, even a skyscraper.
A fun puzzle worthy of a VH rating.

Earl
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Johan



Joined: 25 Jun 2007
Posts: 206
Location: Bornem Belgium

PostPosted: Mon Jan 28, 2008 3:58 pm    Post subject: Reply with quote

This one was indeed a VH rating, the advanced solving sequence I took is an ER on digit <7> in Box 2, takes out <7> in R6C5, then an x-wing <8> in R69C58,

after that an M-wing with the [58] pair in R7C2 and R9C8, eliminating <8> in R8C7 was the final step.
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andras



Joined: 31 Oct 2007
Posts: 56
Location: Mid Wales

PostPosted: Mon Jan 28, 2008 5:38 pm    Post subject: Reply with quote

Johan wrote:
This one was indeed a VH rating, the advanced solving sequence I took is an ER on digit <7> in Box 2, takes out <7> in R6C5, then an x-wing <8> in R69C58,

after that an M-wing with the [58] pair in R7C2 and R9C8, eliminating <8> in R8C7 was the final step.


M-wing? Don't think I've met one of those. Smile

John
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Marty R.



Joined: 12 Feb 2006
Posts: 5728
Location: Rochester, NY, USA

PostPosted: Mon Jan 28, 2008 6:03 pm    Post subject: Reply with quote

andras wrote:
Johan wrote:
This one was indeed a VH rating, the advanced solving sequence I took is an ER on digit <7> in Box 2, takes out <7> in R6C5, then an x-wing <8> in R69C58,

after that an M-wing with the [58] pair in R7C2 and R9C8, eliminating <8> in R8C7 was the final step.


M-wing? Don't think I've met one of those. Smile

John

John,

Try the third post in this thread. Good luck.

Marty

http://www.dailysudoku.co.uk/sudoku/forums/viewtopic.php?t=2143
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cgordon



Joined: 04 May 2007
Posts: 769
Location: ontario, canada

PostPosted: Mon Jan 28, 2008 6:22 pm    Post subject: Reply with quote

Quote:
opens up another xy wing 15-14-45 removes 5 from r1c3


Dead easy at the startl: All I needed were one x-wing, two skyscrapers, one xyz-wing and an ER - but then it got difficult!! In fact I had to resort to the Off-F method (get the answer Off the Forum). Thanks Nataraj for that. Perhaps we need a V VH category or some other new acronym.


Last edited by cgordon on Mon Jan 28, 2008 11:32 pm; edited 1 time in total
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sdq_pete



Joined: 30 Apr 2007
Posts: 119
Location: Rotterdam, NL

PostPosted: Mon Jan 28, 2008 9:25 pm    Post subject: Reply with quote

Found myself curiously error-prone with this one, twice reaching an illogical position following the saved state after basic moves and thinking I must have made a mistake at that stage. Still, on following through carefully enough I got there with the following:
Code:
X   8   R69
XY  578 R6C8   (eliminating 5 in R9C1), and
XY  145 R9C1


Peter
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nataraj



Joined: 03 Aug 2007
Posts: 1047
Location: near Vienna, Austria

PostPosted: Mon Jan 28, 2008 9:36 pm    Post subject: Reply with quote

cgordon wrote:
but then it got difficult!! ... Thanks Nataraj for that. Perhaps we need a VVH category or some other new acronym.


You're welcome - and as you made it to the last hurdle, I'm sure it would have been only a matter of time... Very Happy

The new category - how about "RH" real hard. Hm. What about "vh" then. UNreal hard? Nah, no good. "VrH" very-ER hard? aaarrrggghh!
"XH" ? and then ? XXH?

Actually, I'm quite happy with "vh" as it is. Simply says naked pairs and box/line are not enough. Could do with a little variety sometimes, like vh not solvable by xwing and/or xyz wing, maybe throw in a swordfish or required w-wing at times but come on let's not get picky: we've waited long enough for a "vh" and we were rewarded.
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eddieg



Joined: 12 Jan 2006
Posts: 47
Location: San Diego, CA USA

PostPosted: Mon Jan 28, 2008 10:57 pm    Post subject: Has anybody solved without coloring? Reply with quote

Looking for different solution.
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sheryl



Joined: 24 Sep 2007
Posts: 64
Location: New York

PostPosted: Mon Jan 28, 2008 11:58 pm    Post subject: 1/28 VH Reply with quote

can you tell me where the xy wing on the 14 45 15 is. i have the 14 and the 45 but the only possible 15 that i see that would eliminate the 5 in r1c3 is the 145 in r1c1. if this is a 15 not a 145 can you tell me how you eliminated the 4. thanks a bunch.
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Marty R.



Joined: 12 Feb 2006
Posts: 5728
Location: Rochester, NY, USA

PostPosted: Tue Jan 29, 2008 12:59 am    Post subject: Re: 1/28 VH Reply with quote

sheryl wrote:
can you tell me where the xy wing on the 14 45 15 is. i have the 14 and the 45 but the only possible 15 that i see that would eliminate the 5 in r1c3 is the 145 in r1c1. if this is a 15 not a 145 can you tell me how you eliminated the 4. thanks a bunch.


Sheryl, this is the grid from Norm's post.

Code:
2       1357    56      | 156     167     8       | 4       136     9
147     179     46      | 2       3       179     | 5       16      8
15      1359    8       | 1456    1469    159     | 2       136     7
---------------------------------------------------------------------
9       57      1       | 38      57      6       | 38      2       4
8       6       2       | 134     147     17      | 37      9       5
57      4       3       | 9       58      2       | 6       78      1
---------------------------------------------------------------------
3       58      7       | 568     69      59      | 1       4       2
6       158     9       | 158     2       4       | 78      57      3
145     2       45      | 7       18      3       | 9       58      6


First, play the XY-Wing on 78-58-57 that's pivoted in r6c8. That gets rid of the 5 in r9c1. That cell now becomes the pivot for a 14-45-15 XY-Wing.
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sheryl



Joined: 24 Sep 2007
Posts: 64
Location: New York

PostPosted: Tue Jan 29, 2008 1:04 am    Post subject: today's vh Reply with quote

marty,

i can't read the grid-- it's all squirrily. i don't see how you got rid of the 4 in r3c1(if indeed it's gone). can you explain.
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Marty R.



Joined: 12 Feb 2006
Posts: 5728
Location: Rochester, NY, USA

PostPosted: Tue Jan 29, 2008 1:22 am    Post subject: Re: today's vh Reply with quote

sheryl wrote:
marty,

i can't read the grid-- it's all squirrily. i don't see how you got rid of the 4 in r3c1(if indeed it's gone). can you explain.

Sheryl,

I deeply apologize, but I don't know what a squirrily grid looks like. Laughing It's aligned properly as I look at it.

I also don't remember how I did the puzzle. But looking at Norm's grid, the only possibilities for 4 in row two are in box 1. Therefore, no 4s can exist in box 1 in rows 1 and 3.

Hope that helps.


Last edited by Marty R. on Tue Jan 29, 2008 2:03 am; edited 1 time in total
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sheryl



Joined: 24 Sep 2007
Posts: 64
Location: New York

PostPosted: Tue Jan 29, 2008 1:27 am    Post subject: today's vh Reply with quote

marty,

sorry, i just didn't see it. but now i do see the elimination of the 4 in r3c1. and that finally solved it for me.

thanks for posting all the info. it indeed was a very hard VH!
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sheryl



Joined: 24 Sep 2007
Posts: 64
Location: New York

PostPosted: Tue Jan 29, 2008 1:46 am    Post subject: today's vh Reply with quote

marty,

when i see norm's grid, row 1 is on 2 lines, row 2 is on 2 lines, etc. etc. therefore to me it looks all "squirrelly" and makes it hard to read. If it looks right to you, any ideas why mine would look different?
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Marty R.



Joined: 12 Feb 2006
Posts: 5728
Location: Rochester, NY, USA

PostPosted: Tue Jan 29, 2008 4:46 am    Post subject: Re: today's vh Reply with quote

sheryl wrote:
marty,

when i see norm's grid, row 1 is on 2 lines, row 2 is on 2 lines, etc. etc. therefore to me it looks all "squirrelly" and makes it hard to read. If it looks right to you, any ideas why mine would look different?

No idea. Does it happen with all the grids or just this one? However, if you answer that I wouldn't know what to say anyways.
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