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Earl
Joined: 30 May 2007
Posts: 677
Location: Victoria, KS
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 Posted: Wed Dec 05, 2007 5:26 pm Post subject: Nightmare |
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I'm stuck on the daily nightmare, Help !
Earl
| Code: |
+----------------+-----------------+---------------+
| 7 689 5 | 389 23489 1 | 26 246 49 |
| 2 189 148 | 789 6 4789 | 5 147 3 |
| 1469 169 3 | 5 2479 2479 | 1267 8 479 |
+----------------+-----------------+---------------+
| 8 137 9 | 6 237 5 | 1237 1247 47 |
| 5 4 2 | 378 1 378 | 37 9 6 |
| 16 1367 167 | 4 2379 2379 | 8 127 5 |
+----------------+-----------------+---------------+
| 146 2 1467 | 37 347 3467 | 9 5 8 |
| 3 6789 4678 | 2 5 46789 | 67 67 1 |
| 69 5 678 | 1 789 6789 | 4 3 2 |
+----------------+-----------------+---------------+
|
Play this puzzle online at the Daily Sudoku site |
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re'born
Joined: 28 Oct 2007
Posts: 80
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| Posted: Wed Dec 05, 2007 5:37 pm Post subject: |
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After basics, you get to
| Code: | .------------------.------------------.------------------.
| 7 689 5 | 389 348 1 | 26 246 49 |
| 2 189 48 | 789 6 478 | 5 147 3 |
| 49 16 3 | 5 247 247 | 16 8 479 |
:------------------+------------------+------------------:
| 8 37 9 | 6 237 5 | 1237 1247 47 |
| 5 4 2 | 378 1 378 | 37 9 6 |
| 16 37 16 | 4 2379 2379 | 8 27 5 |
:------------------+------------------+------------------:
| 146 2 167 | 37 347 3467 | 9 5 8 |
| 3 89 48 | 2 5 49 | 67 67 1 |
| 69 5 67 | 1 789 6789 | 4 3 2 |
'------------------'------------------'------------------' |
where there is a potential DP in r67c13 which will eliminate 6 from r7c13. Clean up and there will be a couple of things to do on the candidate 4. Finally look for an xy-wing that eliminates another 4 and the puzzle will be solved. |
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Earl
Joined: 30 May 2007
Posts: 677
Location: Victoria, KS
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| Posted: Wed Dec 05, 2007 6:20 pm Post subject: nightrmare |
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Re'born,
I would appreciate the specifics on the type 2 UR (DP) and how it eliminates 6 from R7C13. Thanks
Earl |
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nataraj
Joined: 03 Aug 2007
Posts: 1048
Location: near Vienna, Austria
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| Posted: Wed Dec 05, 2007 7:02 pm Post subject: |
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Earl,
I don't think it is a type 2 (at least my reference in that matter: http://www.sudoku.com/boards/viewtopic.php?t=2000 says:
| Code: | So the Type-1 Unique Rectangle is:
Code:
12|12A..
12|12
ie:
12|123
12|12
and permits the 12A... to be reduced to A... (A... stands for 1-n other possibilities)
The Type-2 Unique Rectangle is:
Code:
12|123
12|123
and permits 3 to be removed from the common groups (houses) of the 123 squares. If I'm not mistaken, this variant:
Code:
12 |12
123|123
is the Type-2B form (I haven't implemented it yet) and permits removal of 3 from the common group of the 123 squares (in this case, a row)
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I thought this would be a type 3 but I was mistaken...
I think the elimination works like this:
To avoid the DP (16 16) in c13r7, either r7c1=4 or r7c3=7
in both cases r7c6=6.
if r7c1=4, there is a naked pair 3,7 in box 8
if r7c1=7, then r7c4=3 and r7c5=4
_____
edit: it is a type 3 after all (described later in that thread):
| Quote: |
A Type-3 unique rectangle.
12|12A... A... are the 1 or more extra possibilities in one roof square;
12|12B... B... the extras in the other. The quantum-square is the union of A... and B... |
A very comprehensive source of UR-types and explanations: http://www.sudoku.com/boards/viewtopic.php?p=29105#29105 |
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re'born
Joined: 28 Oct 2007
Posts: 80
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| Posted: Wed Dec 05, 2007 8:55 pm Post subject: |
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| Here is how I thought of it: r7c1 = 1 or r7c3 = 1 (since there are only two 1's in row 7) and hence neither of r7c1 or r7c3 can be a 6, else we would have a deadly pattern. |
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ravel
Joined: 21 Apr 2006
Posts: 536
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| Posted: Wed Dec 05, 2007 9:02 pm Post subject: |
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With more words:
The point of this UR type 2 is, that in one line (row or column) you only have the 2 numbers and in the other line a strong link for one number. Then you can eliminate the other number from the second line.
E.g.
| Code: | 12 . 12
. . .
. . .
-----------------
12345 . 1235789
No other 2 in this line -> eliminate 1 here |
Reasoning:
A pattern
| Code: | 1.2
...
...
-----
2.1 |
always is deadly, if none of the 4 numbers is a given, because no 1 or 2 can be in the same row, column or box. That means, if this pattern is possible, you always can exchange the numbers to get a second solution.
Now because of the strong link for 2 a 1 in the second line just would lead to this pattern. |
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storm_norm
Joined: 18 Oct 2007
Posts: 1741
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| Posted: Wed Dec 05, 2007 9:07 pm Post subject: |
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| Code: | ------------------------------------------------------------------------------|
| 7 689 5 | 389 348# 1 | 26 246 49 |
| 2 189 48 | 789 6 478 | 5 147 3 |
| 49# 16 3 | 5 247# 27-4 | 16 8 479 |
------------------------------------------------------------------------------|
| 8 37 9 | 6 237 5 | 1237 1247 47 |
| 5 4 2 | 378 1 378 | 37 9 6 |
| 16 37 16 | 4 2379 2379 | 8 27 5 |
------------------------------------------------------------------------------|
| 146# 2 167 | 37 347# 3467 | 9 5 8 |
| 3 89 48 | 2 5 49 | 76 76 1 |
| 69 5 76 | 1 789 6789 | 4 3 2 |
------------------------------------------------------------------------------|
# is finned x-wing on 4, takes out 4 in r3c6 |
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storm_norm
Joined: 18 Oct 2007
Posts: 1741
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| Posted: Wed Dec 05, 2007 9:12 pm Post subject: |
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so the UR takes out the 6's in r7c13 ???
then if that is the case, there is an x-wing on 4 that takes out a 4 in r2c8 |
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nataraj
Joined: 03 Aug 2007
Posts: 1048
Location: near Vienna, Austria
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| Posted: Wed Dec 05, 2007 9:36 pm Post subject: |
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| ravel wrote: | | The point of this UR type 2 is, that in one line (row or column) you only have the 2 numbers and in the other line a strong link for one number. Then you can eliminate the other number from the second line. |
That is a VERY useful rule. I'll remember it. |
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ravel
Joined: 21 Apr 2006
Posts: 536
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| Posted: Wed Dec 05, 2007 9:49 pm Post subject: |
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| Thanks, but i am not sure now, if this isn't type 4. Anyway you can use the same reasoning for all types, that make eliminations of the UR candidates themselves (e.g. type 6). |
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Marty R.
Joined: 12 Feb 2006
Posts: 5770
Location: Rochester, NY, USA
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| Posted: Wed Dec 05, 2007 10:29 pm Post subject: |
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| storm_norm wrote: | so the UR takes out the 6's in r7c13 ???
then if that is the case, there is an x-wing on 4 that takes out a 4 in r2c8 |
| Code: | .------------------.------------------.------------------.
| 7 689 5 | 389 348 1 | 26 246 49 |
| 2 189 48 | 789 6 478 | 5 147 3 |
| 49 16 3 | 5 247 247 | 16 8 479 |
:------------------+------------------+------------------:
| 8 37 9 | 6 237 5 | 1237 1247 47 |
| 5 4 2 | 378 1 378 | 37 9 6 |
| 16 37 16 | 4 2379 2379 | 8 27 5 |
:------------------+------------------+------------------:
| 146 2 167 | 37 347 3467 | 9 5 8 |
| 3 89 48 | 2 5 49 | 67 67 1 |
| 69 5 67 | 1 789 6789 | 4 3 2 |
'------------------'------------------'------------------' |
I believe this is a Type 3. The technique I learned for this situation was called a "reduced set." One of the two roof cells must be = 4 or 7. These two cells combine with r7c45 to be a de facto 347 triple, thus solving r7c6 = 6. I don't see many of these but they're fun when they do appear. |
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ravel
Joined: 21 Apr 2006
Posts: 536
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| Posted: Wed Dec 05, 2007 11:02 pm Post subject: |
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| You are right, its also a type 3. |
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Marty R.
Joined: 12 Feb 2006
Posts: 5770
Location: Rochester, NY, USA
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| Posted: Thu Dec 06, 2007 12:35 am Post subject: |
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| Re: my comments two posts above: I did not notice at the time that this was a Type 4 with a strong link on 1. |
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