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Oct 21 "vh" - medium at best
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nataraj



Joined: 03 Aug 2007
Posts: 1048
Location: near Vienna, Austria

PostPosted: Sun Oct 21, 2007 8:39 am    Post subject: Oct 21 "vh" - medium at best Reply with quote

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

wrong rating or wrong puzzle.
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nataraj



Joined: 03 Aug 2007
Posts: 1048
Location: near Vienna, Austria

PostPosted: Sun Oct 21, 2007 8:53 am    Post subject: Reply with quote

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:

Code:

+--------------------------+--------------------------+--------------------------+
| 135     2       67       | 178     1378    9        | 4       1367    58       |
| 1345    15      47       | 2       6       1348     | 58      137     9        |
| 8       169     4679     | 147     137     5        | 2       1367    167      |
+--------------------------+--------------------------+--------------------------+
| 7       1689    5        | 189     12389   12368    | 689     4       268      |
| 129     3       2689     | 1789    4       1268     | 689     5       2678     |
| 29      4       2689     | 5       2789    268      | 1       267     3        |
+--------------------------+--------------------------+--------------------------+
| 259     589     3        | 6       1289    128      | 7       129     4        |
| 6       89      2489     | 1489    5       7        | 3       129     12       |
| 249     7       1        | 3       29      24       | 56      8       56       |
+--------------------------+--------------------------+--------------------------+


Expect coloring and xy-wing but nothing too heavy.

Enjoy!
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cgordon



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

PostPosted: Sun Oct 21, 2007 9:01 pm    Post subject: Reply with quote

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.
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Marty R.



Joined: 12 Feb 2006
Posts: 5770
Location: Rochester, NY, USA

PostPosted: Sun Oct 21, 2007 9:08 pm    Post subject: Reply with quote

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



Joined: 05 Jun 2007
Posts: 865
Location: Sonoma County, CA, USA

PostPosted: Sun Oct 21, 2007 9:21 pm    Post subject: Reply with quote

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
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keith



Joined: 19 Sep 2005
Posts: 3355
Location: near Detroit, Michigan, USA

PostPosted: Sun Oct 21, 2007 9:23 pm    Post subject: Reply with quote

This is the starting position.
Code:
+----------------------+----------------------+----------------------+
| 1      36     5      | 4      8      379    | 239    239    239    |
| 38     34     348    | 1359   2      1359   | 7      6      1349   |
| 2368   7      9      | 1356   156    135    | 23458  2345   1234   |
+----------------------+----------------------+----------------------+
| 36789  369    3678   | 2      467    3479   | 349    1      5      |
| 35679  2      367    | 135679 14567  134579 | 349    8      34679  |
| 4      1      367    | 35679  567    8      | 239    239    23679  |
+----------------------+----------------------+----------------------+
| 2359   3459   234    | 158    145    1245   | 6      7      2349   |
| 23567  8      1      | 57     9      2457   | 2345   2345   234    |
| 2579   459    247    | 57     3      6      | 1      2459   8      |
+----------------------+----------------------+----------------------+

The solution does not require any "advanced" moves. You only have to find the pairs, triples, and/or intersections in B456.

Keith
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Asellus



Joined: 05 Jun 2007
Posts: 865
Location: Sonoma County, CA, USA

PostPosted: Sun Oct 21, 2007 9:39 pm    Post subject: Reply with quote

I should clarify...

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



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

PostPosted: Sun Oct 21, 2007 10:59 pm    Post subject: i think its hard Reply with quote

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 |
+------------+-----------------+----------------+
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Marty R.



Joined: 12 Feb 2006
Posts: 5770
Location: Rochester, NY, USA

PostPosted: Sun Oct 21, 2007 11:40 pm    Post subject: Re: i think its hard Reply with quote

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

Code:
+------------+-----------------+----------------+
| 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     |
+------------+-----------------+----------------+
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sheryl



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

PostPosted: Sun Oct 21, 2007 11:57 pm    Post subject: oct. 21 vh? Reply with quote

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.
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kragzy



Joined: 01 May 2007
Posts: 112
Location: Australia

PostPosted: Mon Oct 22, 2007 12:30 am    Post subject: Reply with quote

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
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Asellus



Joined: 05 Jun 2007
Posts: 865
Location: Sonoma County, CA, USA

PostPosted: Mon Oct 22, 2007 12:37 am    Post subject: Reply with quote

Sheryl,

Let's make certain you are viewing the XY Wing correctly:
Code:
+-------------+-----------------+----------------+
| 1   6  5    | 4    8     7    | 9    3   2     |
|#38 p34 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 |
+-------------+-----------------+----------------+
|p39  5  234  | 8    14    124  | 6    7   139   |
| 6   8  1    | 7    9     2    | 5    4   3     |
| 79 v49 247  | 5    3     6    | 1    249 8     |
+-------------+-----------------+----------------+

The pivot is marked "v". The two pincers are marked "p". The victim is marked #.

If the pivot is <4>, the pincer in Row 2 is <3>. Alternately, if the pivot is <9>, the pincer in Row 7 is <3>. Since one of these two alternatives must be true, the victim cell cannot contain <3>.

This isn't guesswork because it's a well-established pattern that has a clear logic. As sudoku techniques go, it is one of the easier to spot and apply. It might help to read this:
http://www.sudocue.net/guide.php#XYWing
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kragzy



Joined: 01 May 2007
Posts: 112
Location: Australia

PostPosted: Mon Oct 22, 2007 12:44 am    Post subject: Reply with quote

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.
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Asellus



Joined: 05 Jun 2007
Posts: 865
Location: Sonoma County, CA, USA

PostPosted: Mon Oct 22, 2007 12:45 am    Post subject: Reply with quote

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.
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keith



Joined: 19 Sep 2005
Posts: 3355
Location: near Detroit, Michigan, USA

PostPosted: Mon Oct 22, 2007 1:49 am    Post subject: Re: i think its hard Reply with quote

sheryl wrote:
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 |
+------------+-----------------+----------------+


Sheryl:

R6C9 is the only cell in row 6 that can be <8>.

R7C6 is the only cell in column 6 that can be <2>.

R6C7 is the only cell in column 7 that can be <2>.

R6C8 is the only cell in column 8 that can be <3>.

R9C8 is the only cell in column 8 that can be <4>.

R7C9 is the only cell in column 9 that can be <1>.

R4C2 is the only cell in block 4 that can be <9>.


Keith
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kragzy



Joined: 01 May 2007
Posts: 112
Location: Australia

PostPosted: Mon Oct 22, 2007 3:05 am    Post subject: Reply with quote

Keith,

wrong
wrong
right
wrong
wrong
wrong
right

Check the cells that re already solved.

Cheers
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duffy



Joined: 13 Sep 2007
Posts: 26
Location: Toronto Canada

PostPosted: Mon Oct 22, 2007 3:07 am    Post subject: Reply with quote

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. Wink

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!
Rolling Eyes
Don D.
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duffy



Joined: 13 Sep 2007
Posts: 26
Location: Toronto Canada

PostPosted: Mon Oct 22, 2007 3:16 am    Post subject: Reply with quote

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.
Idea
Don D.
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sheryl



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

PostPosted: Mon Oct 22, 2007 3:23 am    Post subject: Reply with quote

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!!!
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keith



Joined: 19 Sep 2005
Posts: 3355
Location: near Detroit, Michigan, USA

PostPosted: Mon Oct 22, 2007 3:31 am    Post subject: Reply with quote

(revised Oct 23, 2007)

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

Here are the correct candidates:

Code:
+----------------+----------------+----------------+
| 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    |
+----------------+----------------+----------------+
| 3789 39   3678 | 2    467  349  | 34   1    5    |
| 5    2    367  | 136  1467 1349 | 34   8    679  |
| 4    1    367  | 36   5    8    | 23   29   679  |
+----------------+----------------+----------------+
| 39   5    234  | 8    14   14   | 6    7    9    |
| 6    8    1    | 7    9    2    | 5    4    3    |
| 79   49   247  | 5    3    6    | 1    29   8    |
+----------------+----------------+----------------+


R7C9 must be <9>.
R7C3 is the only square in row 7 that can be <2>.
R6C7 is the only square in column 7 that can be <2>.
R9C8 is the only square in block 9 that can be <2>.

Keith


Last edited by keith on Wed Oct 24, 2007 9:25 am; edited 2 times in total
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