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DB Saturday Puzzle - May 13, 2006

 
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keith



Joined: 19 Sep 2005
Posts: 3150
Location: near Detroit, Michigan, USA

PostPosted: Sat May 13, 2006 2:09 pm    Post subject: DB Saturday Puzzle - May 13, 2006 Reply with quote

Here is today's David Bodycombe puzzle. A tough one!

Code:

Puzzle: DB051306  ******
+-------+-------+-------+
| . . 3 | 4 . 5 | . . . |
| . 8 . | . 9 7 | . 3 2 |
| 9 . . | . 8 . | . . . |
+-------+-------+-------+
| . . 8 | . . . | . . 6 |
| 1 6 . | . 4 . | . 9 3 |
| 3 . . | . . . | 4 . . |
+-------+-------+-------+
| . . . | . 5 . | . . 7 |
| 5 2 . | 9 3 . | . 8 . |
| . . . | 8 . 2 | 9 . . |
+-------+-------+-------+

Or, if you want the possibilities filled in:
Code:

+----------------------+----------------------+----------------------+
| 267    17     3      | 4      126    5      | 1678   167    189    |
| 46     8      1456   | 16     9      7      | 156    3      2      |
| 9      1457   124567 | 1236   8      136    | 1567   14567  145    |
+----------------------+----------------------+----------------------+
| 247    4579   8      | 12357  127    139    | 1257   1257   6      |
| 1      6      257    | 257    4      8      | 2578   9      3      |
| 3      579    2579   | 12567  1267   1689   | 4      1257   158    |
+----------------------+----------------------+----------------------+
| 468    1349   1469   | 16     5      146    | 1236   1246   7      |
| 5      2      1467   | 9      3      146    | 16     8      14     |
| 467    1347   1467   | 8      167    2      | 9      1456   145    |
+----------------------+----------------------+----------------------+

Best wishes,

Keith
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Marty R.



Joined: 12 Feb 2006
Posts: 5121
Location: Rochester, NY, USA

PostPosted: Sat May 13, 2006 9:05 pm    Post subject: Reply with quote

For what it's worth, here's my take on it. During the initial scan of bands and stacks, five cells were solved. Five more cells were then solved during the drudgery of filling in cells with their candidates.

After standard elimination techniques, I couldn't find any block interactions, X-Wings, finned or otherwise, strong links, coloring or XY-Wings. I didn't do a complete check for 3-, 4- or 5-fish because I hate doing it because of all the work.

At that point, a two-candidate cell looked promising, so I started--take your choice--a forcing chain or DIC. One of the values led to a contradiction, so with that cell solved, standard techniques solved more cells to the point where a unique rectangle opened up and that finished off the puzzle.

I enjoy these and hope you continue to post them.
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keith



Joined: 19 Sep 2005
Posts: 3150
Location: near Detroit, Michigan, USA

PostPosted: Sat May 13, 2006 9:51 pm    Post subject: On DB Puzzles Reply with quote

Hi, Marty!

You said:

Quote:

... I didn't do a complete check for 3-, 4- or 5-fish because I hate doing it because of all the work.
...
I enjoy these and hope you continue to post them.

Actually, you do not need to check for 5-fish, if you check both rows and columns.

If you find a fish in the columns (rows), there is always a complementary fish in the rows (columns) that makes the same eliminations!

Assume the fish is on the value <7>. There are nine cells that have <7> in the solution. If none of the <7>'s are solved, the worst case is there can be a 5-fish (squirmbag) in one direction, and a 4-fish (jellyfish) in the other.

In reality, it is unlikely that you will find enough strong links to make fishes unless the puzzle is substantially solved.

Let's say you have solved three cells with <7>. The remaining six can form at most two 3-fish (swordfish), but are more likely a 2-fish (X-wing) and a 4-fish.

In my opinion, if you look for X-wings in both the rows and columns, you will almost never need to look for swordfish.

As for your last comment, thank you. I am not in the business of republishing these (copyright!), but I do post the ones I think are more challenging.

Best wishes,

Keith
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Marty R.



Joined: 12 Feb 2006
Posts: 5121
Location: Rochester, NY, USA

PostPosted: Sun May 14, 2006 4:13 pm    Post subject: Reply with quote

Quote:
Actually, you do not need to check for 5-fish, if you check both rows and columns.

One of the things I have to work on is checking columns. I do fine on rows, but I have trouble visualizing things in columns. And rotating the puzzle 90 doesn't do it because of the trouble reading the numbers.

Quote:
In my opinion, if you look for X-wings in both the rows and columns, you will almost never need to look for swordfish.

I think what you're saying is that if time were money, looking for swordfish and more is cost-prohibitive and needn't be done except as a desperation, last-resort tactic.

Quote:
As for your last comment, thank you. I am not in the business of republishing these (copyright!), but I do post the ones I think are more challenging.

I've often wondered if people could legally be enjoined from posting such material. But if they could be, I hope that doesn't deter you.

Happy Mother's Day! Very Happy
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keith



Joined: 19 Sep 2005
Posts: 3150
Location: near Detroit, Michigan, USA

PostPosted: Mon May 15, 2006 12:26 am    Post subject: My tips Reply with quote

Hi, Marty:

Quote:
One of the things I have to work on is checking columns. I do fine on rows, but I have trouble visualizing things in columns. And rotating the puzzle 90 doesn't do it because of the trouble reading the numbers.

When you find a conjugate pair (strong link) in a row or column, write that value next to the row (column) on the outside of the puzzle. This makes it much easier to do coloring or look for X-wings later.

Quote:
I think what you're saying is that if time were money, looking for swordfish and more is cost-prohibitive and needn't be done except as a desperation, last-resort tactic.

Yes! With X-wings, strong links, and simple coloring, you will catch swordfish without realizing it.

Quote:
I've often wondered if people could legally be enjoined from posting such material. But if they could be, I hope that doesn't deter you.

If someone complained, I would stop. But, these puzzles are not otherwise available online, Mr Bodycombe always gets credit, and I do not gain. No harm done, in my opinion.

Quote:
Happy Mother's Day!

By the way, I am golden for Mother's Day. I mowed the lawn, and cooked dinner for the Wife and her Mother. Did I say that I also bought the roses, yesterday?

Best wishes,

Keith
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Marty R.



Joined: 12 Feb 2006
Posts: 5121
Location: Rochester, NY, USA

PostPosted: Mon May 15, 2006 3:43 pm    Post subject: Reply with quote

Thanks for the tips.

Quote:
By the way, I am golden for Mother's Day. I mowed the lawn, and cooked dinner for the Wife and her Mother. Did I say that I also bought the roses, yesterday?


Well, I mowed the lawn. Smile
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