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DB Saturday Puzzle: July 21, 2007

 
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keith



Joined: 19 Sep 2005
Posts: 3179
Location: near Detroit, Michigan, USA

PostPosted: Sat Jul 21, 2007 11:01 am    Post subject: DB Saturday Puzzle: July 21, 2007 Reply with quote

It's fairly obvious where this one is going, but I found a Franken swordfish!

Keith

Code:
Puzzle: DB072107  ******
+-------+-------+-------+
| . . 7 | 4 . . | . . 9 |
| 6 . . | . 7 9 | 1 . . |
| . . 1 | . . . | 4 7 . |
+-------+-------+-------+
| 3 . . | . . . | . 6 . |
| 4 . . | 3 9 2 | . . 1 |
| . 1 . | . . . | . . 2 |
+-------+-------+-------+
| . 8 3 | . . . | 6 . . |
| . . 4 | 6 2 . | . . 3 |
| 1 . . | . . 4 | 9 . . |
+-------+-------+-------+
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Mogulmeister



Joined: 03 May 2007
Posts: 695

PostPosted: Sat Jul 21, 2007 11:06 am    Post subject: Reply with quote

(Keith - please explain for the benefit of those reading who are "non-fished up") Smile


How does a frankenfish differ from a regular swordfish, jellyfish etc ?
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keith



Joined: 19 Sep 2005
Posts: 3179
Location: near Detroit, Michigan, USA

PostPosted: Sat Jul 21, 2007 11:31 am    Post subject: Frankenfish Reply with quote

MM,

I posted an example in the Solving Techniques forum:

http://www.dailysudoku.com/sudoku/forums/viewtopic.php?t=1978&sid=2

In today's puzzle, after the basics, find an X-wing that makes one elimination. Then, the franken swordfish can be seen swimming.

Keith
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Earl



Joined: 30 May 2007
Posts: 546
Location: St Louis MO

PostPosted: Sat Jul 21, 2007 6:36 pm    Post subject: DB July 21 Reply with quote

I solved it quickly with UR's.
First eliminating 7 in R9C2, and then R5C2 must be 7.

It went so easy, I am concerned I might have made a wrong assumption or a mistake.

Earl
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keith



Joined: 19 Sep 2005
Posts: 3179
Location: near Detroit, Michigan, USA

PostPosted: Sat Jul 21, 2007 7:07 pm    Post subject: UR Eliminations Reply with quote

Earl,

The basics get you to here:
Code:
+-------------+-------------+-------------+
| 58  3   7   | 4   6   1   | 2   58  9   |
| 6   4   2   | 58  7   9   | 1   3   58  |
| 589 59  1   | 2   58  3   | 4   7   6   |
+-------------+-------------+-------------+
| 3   2   9   | 1   58  578 | 578 6   4   |
| 4   567 568 | 3   9   2   | 578 58  1   |
| 57  1   58  | 578 4   6   | 3   9   2   |
+-------------+-------------+-------------+
| 2   8   3   | 9   1   57  | 6   4   57  |
| 579 579 4   | 6   2   578 | 58  1   3   |
| 1   567 56  | 578 3   4   | 9   2   578 |
+-------------+-------------+-------------+

Note that the unsolved cells for <6> are an X-wing. They are also a UR on <56>. You can eliminate <5> in R5C2.

The same goes for the unsolved cells for <9>. They are a UR on <59>. You can eliminate <5> in R8C1.

Except, this does really not help to solve the puzzle.

I do not see how to make your elimination of <7> in R9C2.

Best wishes,

Keith
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Earl



Joined: 30 May 2007
Posts: 546
Location: St Louis MO

PostPosted: Sat Jul 21, 2007 9:45 pm    Post subject: DB July 21 Reply with quote

Keith,

Using your posted grid, and X wing in 8's (R2,9) eliminates 8 in R6C4 and then R6C3 = 8.

A UR (5Cool in R2,9 demands that R9C4 or 9 = 7 so that R9C2 = 56.
Then UR (56) in R4,9 demands that R4C2 = 7.
Rest is simple elimination.

(Now I am doubting if a UR in four boxes is valid?)
I am a novice with these techniques.

Anyway, it worked!

Earl
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Marty R.



Joined: 12 Feb 2006
Posts: 5166
Location: Rochester, NY, USA

PostPosted: Sat Jul 21, 2007 9:52 pm    Post subject: Reply with quote

Nine cells with 58 were driving me nuts. It took me five moves:

1) Skyscraper on 5
2) X-Wing on 8 (which you didn't use or didn't see, Keith)
3) Type 2 rectangle on 56
4) Type 4 rectangle on 59
5) Skyscraper on 7 finishes it off

Quote:
(Now I am doubting if a UR in four boxes is valid?)


Earl, the principles of URs are valid only when the rectangle is in two boxes, or stated differently, it must be in the same band or stack. Keith's primer on rectangles is at:

http://www.sudoku.com/forums/viewtopic.php?p=29105#29105
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keith



Joined: 19 Sep 2005
Posts: 3179
Location: near Detroit, Michigan, USA

PostPosted: Sat Jul 21, 2007 10:37 pm    Post subject: Reply with quote

Marty,

When I said "you can see where this is going", it was a reference to the <58> pairs. Indeed, there is a remote naked pair, starting in "a" and ending in "C". (aAbBcC.) It takes out <58> in R4C7, and the puzzle is done!

Code:
+-------------+-------------+--------------+
| 58  3   7   | 4   6   1   | 2    58c 9   |
| 6   4   2   | 58b 7   9   | 1    3   58B |
| 589 59  1   | 2   58A 3   | 4    7   6   |
+-------------+-------------+-------------+
| 3   2   9   | 1   58a 578 | 578# 6   4   |
| 4   567 568 | 3   9   2   | 578  58C 1   |
| 57  1   58  | 578 4   6   | 3    9   2   |
+-------------+-------------+--------------+
| 2   8   3   | 9   1   57  | 6    4   57  |
| 579 579 4   | 6   2   578 | 58   1   3   |
| 1   567 56  | 578 3   4   | 9    2   578 |
+-------------+-------------+--------------+


Actually, I did see the X-wing on <8>. It leads to the franken swordfish. The X-wing in R29C49 takes out <8> in R6C4. Following a simplification in R6, you have:
Code:
+---------------+-------------+-------------+
| 58a   3   7   | 4    6   1   | 2   58A  9   |
| 6    4   2   | 58b   7   9   | 1   3   58B  |
| 589# 59  1   | 2    58  3   | 4   7   6   |
+-------------+--------------+-------------+
| 3    2   9   | 1    58  578 | 578 6   4   |
| 4    567 56  | 3    9   2   | 578 58  1   |
| 57c   1   8   | 57C   4   6   | 3   9   2   |
+--------------+--------------+-------------+
| 2    8   3   | 9   1    57  | 6   4   57  |
| 579# 579 4   | 6    2   578 | 58  1   3   |
| 1    567 56  | 578# 3   4   | 9   2   578 |
+--------------+--------------+-------------+


There are strong links on <5> in R126. They line up in C14 and B3. The eliminations are <5> in the cells marked #.

At least, this morning, I thought this solved the puzzle. I don't see it right now.

Keith
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Marty R.



Joined: 12 Feb 2006
Posts: 5166
Location: Rochester, NY, USA

PostPosted: Sat Jul 21, 2007 11:23 pm    Post subject: Reply with quote

Quote:
Actually, I did see the X-wing on <8>.


I should have known better than to even suggest that you missed something. Embarassed

As to the remote pairs, I don't recall if I looked at the 58 cells for them. I do recall that I unsuccessfully looked at them for W-Wings.
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Earl



Joined: 30 May 2007
Posts: 546
Location: St Louis MO

PostPosted: Sun Jul 22, 2007 1:52 am    Post subject: DB July 21 Reply with quote

Marty,

Thanks for the correction on UR.
I thought it went to0 easy.
But then I found a valid way.

Basic moves got me here:

Code:

+------------+------------+------------+
| 58  3   7  | 4   6  1   | 2   58 9   |
| 6   4   2  | 58  7  9   | 1   3  58  |
| 589 59  1  | 2   58 3   | 4   7  6   |
+------------+------------+------------+
| 3   2   9  | 1   58 578 | 578 6  4   |
| 4   567 56 | 3   9  2   | 578 58 1   |
| 57  1   8  | 57  4  6   | 3   9  2   |
+------------+------------+------------+
| 2   8   3  | 9   1  57  | 6   4  57  |
| 579 579 4  | 6   2  578 | 578 1  3   |
| 1   567 56 | 578 3  4   | 9   2  578 |
+------------+------------+------------+

Play this puzzle online at the Daily Sudoku site


Then a VALID UR (56) removed 7 from R8C2,
a skyscraper of 7's removed 7 from R6C1,
and the rest was simple elimination.

I think.

Earl

PS I could not see the fish. Someone give me a hint.
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