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Dec 28 - v. hard

 
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PoppaPoppa



Joined: 06 Nov 2005
Posts: 21
Location: Arkansas USA
PostPosted: Wed Dec 28, 2005 7:27 pm    Post subject: Dec 28 - v. hard Reply with quote
Very hard indeed. Can anyone tell me why the "hint" places a 9 in r6c6 after this position? Confused

070 520 630
050 000 070
900 008 002
017 004 000
090 000 060
000 800 310
109 600 005
040 000 096
086 095 003
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someone_somewhere



Joined: 07 Aug 2005
Posts: 275
Location: Munich
PostPosted: Wed Dec 28, 2005 11:18 pm    Post subject: Reply with quote
Hi,

Follow the path:

Code:
 1 not in r2c7, it is in r1c9 or r2c9 (Column on 3x3 Block interaction)
 1 not in r3c7, it is in r1c9 or r2c9 (Column on 3x3 Block interaction)
 7 not in r5c7, it is in r5c9 or r6c9 (Column on 3x3 Block interaction)
 4 not in r3c3, Nacked Pair 4 5 in r3c7 and r3c8 (same Row)
 4 not in r3c4, Nacked Pair 4 5 in r3c7 and r3c8 (same Row)
 4 not in r3c5, Nacked Pair 4 5 in r3c7 and r3c8 (same Row)
 4 not in r1c9, it is in r3c7 or r3c8 (Row on 3x3 Block interaction)
 4 not in r2c7, it is in r3c7 or r3c8 (Row on 3x3 Block interaction)
 4 not in r2c9, it is in r3c7 or r3c8 (Row on 3x3 Block interaction)
 4 not in r2c1, it is in r1c1 or r1c3 (Row on 3x3 Block interaction)
 4 not in r2c3, it is in r1c1 or r1c3 (Row on 3x3 Block interaction)
 4 not in r5c7, it is in r5c9 or r6c9 (Column on 3x3 Block interaction)
 8 not in r5c9, Hidden Pair 4 7 in r5c9 and r6c9 (in Column)
 9 not in r6c9, Hidden Pair 4 7 in r5c9 and r6c9 (in Column)

9 in r6c6 - Unique Horizontal

hope that helped.

see u,
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Guest
PostPosted: Thu Dec 29, 2005 12:10 am    Post subject: huh? Reply with quote
I do not get this logic at all.....

Quote:
Code:
 
 4 not in r3c3, Nacked Pair 4 5 in r3c7 and r3c8 (same Row)
 4 not in r3c4, Nacked Pair 4 5 in r3c7 and r3c8 (same Row)
 4 not in r3c5, Nacked Pair 4 5 in r3c7 and r3c8 (same Row)

9 in r6c6 - Unique Horizontal

hope that helped.

see u,


seems to me any of those could be a 4
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someone_somewhere



Joined: 07 Aug 2005
Posts: 275
Location: Munich
PostPosted: Thu Dec 29, 2005 7:48 am    Post subject: Reply with quote
Hi,

Ok.
Let's take a deep look at the 6-th 3x3 block, with the corners: r4c7-r4c9-r6c9-r6c7.
Digit 7 is in r2c8. So it can't be in r7c8 and can't be in r9c8. So, it must be r7c7, r8c7 or r9c7 (it has to be one of the boxes of the 9-th 3x3 block).
This leaves us for digit 7 in the 6-th block only: r5c9 or r6c9.

Now let's concetrate on digit 4.
From 1-st 3x3 box we know that it has to be in r1c1 or r1c4. So it can't be in r1c9.
From 2-dt 3x3 box we know that it has to be in r2c4 or r2c5. So it can't be in r2c9.
4 is in r4c6.
So we have to have a 4 in column 9 and the only posibilities left are r5c9 or r6c9.
So 4 can't be in any other place of the 6-th 3x3 block.

Now we have our Hidden Pair 4, 7 in r5c9 and r6c9.

Hope this could help.

see u,
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Guest
PostPosted: Thu Dec 29, 2005 2:44 pm    Post subject: Reply with quote
Hi,

One question about r3c7 and r3c8.

How did you remove 8 as a possibility to get 4 and 5 as a nacked pair?

Thanks!
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ADBjester



Joined: 28 Dec 2005
Posts: 3
PostPosted: Thu Dec 29, 2005 3:44 pm    Post subject: Reply with quote
Anonymous wrote:
Hi,

One question about r3c7 and r3c8.

How did you remove 8 as a possibility to get 4 and 5 as a nacked pair?



Ummmm..... perhaps I don't understand your question. r3c6 is a natural 8 (given by the author). Therefore r3c7 and r3c8 cannot be an 8.

I admit, I got stuck here too, for quite some time. My crosshatching was incomplete and did not allow me to find the pairs and triples needed to progress. This is "very hard" because there's a series of progressive pairs and hidden pairs, each one unlocked by the prior.

Running the puzzle through Su Doku Sensei (since I didn't want to spend the time to transpose this all) shows that you should be in the following state once crosshatching is complete. Here's the state of the puzzle (including possibilities) after all cross-hatching has taken you as far as you can go and you then MUST start using pairs and triples to progress further.

If you Haven't narrowed down to this state yet, keep looking for additional simple candidate eliminations through cross-hatching.

Code:

...     1..            1..            1..
4..  7  4..     5   2  ...     6   3  4..
.8.     .8.            ..9            .89

.23     123    1.3 1.3 1.3    1..     1..
4.6  5  4..    4.. 4.6 ..6    4..  7  4..
.8.     .8.    ..9 ... ..9    .89     .89

    ..3 1.3    1.3 1.3        1.. ...
 9  ..6 4..    4.. 4.6  8     45. 45.  2
    ... ...    7.. 7..        ... ...


.23            .23 ..3        .2. .2. ...
.56  1   7     ... .56  4     .5. .5. ...
.8.            ..9 ...        .89 .8. .89

.23     .23    123 1.3 123    .2.     ...
45.  9  45.    ... .5. ...    45.  6  4..
.8.     .8.    7.. 7.. 7..    78.     78.

.2. .2. .2.        ... .2.            ...
456 ..6 45.     8  .56 ..6     3   1  4..
... ... ...        7.. 7.9            7.9


    .23            ..3 .23    .2. .2.
 1  ...  9      6  4.. ...    4.. 4..  5
    ...            78. 7..    78. .8.

.23     .23    123 1.3 123    12.
.5.  4  .5.    ... ... ...    ...  9   6
7..     ...    7.. 78. 7..    78.

.2.            12.            12. .2.
...  8   6     4..  9   5     4.. 4..  3
7..            7..            7.. ...


From here, the steps are:

1 claims column 7, lower right box. No 1's possible elsewhere in c7 top
7 claims column 9, middle right box. No 7 possible in r5c7
Row 3 (4,5) pair. Remove other 4's from upper right box.
Row 3 (4,5) pair claims 4 that row. Remove other 4's from Row 3.
Column 9, hidden pair (4,7), remove 8 from r5c9, remove 9 from r6c9

Bang, you have now removed all nines from row 6, save column 6. You can now place the nine you asked about.

Good luck!

Jester
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Steve R



Joined: 24 Oct 2005
Posts: 289
Location: Birmingham, England
PostPosted: Thu Dec 29, 2005 9:21 pm    Post subject: Take Wing? Reply with quote
I got seriously held up on this one too, probably at much the same point as PoppaPoppa. Some hours later….

There are only two places for a 9 in the first row. It must lie in column 6 or column 9. The same applies to the sixth row. This X-Wing eliminates 9 from r4c9, leaving 8 as the only admissible entry. The continuation is mundane.

Before reading the excellent discussion, I really thought samgj had taken off for the first time, at least in public.

Steve
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PoppaPoppa



Joined: 06 Nov 2005
Posts: 21
Location: Arkansas USA
PostPosted: Fri Dec 30, 2005 12:35 am    Post subject: Sudoku sensi Reply with quote
Getting a tip from ADB Jester, I downloaded the Sudoku Sensi 1.03 from the site http://sourceforge.net/projects/sudoku-sensei/ but cannot find the executable after unpacking the zip files... anyone know what to do? Is it the .dev files? How does one execute these under Windows XP?

Thanks
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PoppaPoppa



Joined: 06 Nov 2005
Posts: 21
Location: Arkansas USA
PostPosted: Fri Dec 30, 2005 2:15 am    Post subject: Thanks Reply with quote
Thx to all for the help on Dec 28 puzzle - Jester and Steve R. were really really helpful Very Happy
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