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May 29th very hard puzzle
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geogecko



Joined: 04 Jul 2006
Posts: 5

PostPosted: Wed Jul 05, 2006 1:14 am    Post subject: Reply with quote

Laughing Are you kidding me? How many techniques must one learn?!

The Swordfish?!

Oh, I see you have edited your post. Thanks for the links! I will surely need them for this monster...

It seems that the "Very Hard" class ranges quite a bit. I have solved several of the Very Hard's just using the basic techniques, along with double, tripple and quad matching.

This is the first puzzle that I've used and learned about, the X-Wing, and now about the rest of these. Interesting.
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TKiel



Joined: 22 Feb 2006
Posts: 292
Location: Kalamazoo, MI

PostPosted: Wed Jul 05, 2006 1:23 am    Post subject: Reply with quote

Geogecko,

Until recently the 'Very Hard' on this site could be solved with nothing more complicated than triples. Recently the software was modified to recognize x-wing.

A swordfish is the same concept as an x-wing except it occurs in three rows and 3 columns and can have up to three cells that can contain the digit. There is also a deep-sea creature for 4-4-4 (jellyfish) and 5-5-5 (either starfish or squirmbag). It's not so hard to keep track of once you decide to devote every waking moment to it.
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keith



Joined: 19 Sep 2005
Posts: 3184
Location: near Detroit, Michigan, USA

PostPosted: Wed Jul 05, 2006 1:58 am    Post subject: The next step Reply with quote

geogecko,

To go beyond the basics, you should learn about Strong Links, also known as Conjugate Pairs. Look at:

http://www.sudoku.com/forums/viewtopic.php?t=3326

These are the basis of many advanced techniques (which you will then not need to learn individually).

Keith

Memo to Tracy: Every waking moment? You've never dreamt about these stupid puzzles? I have! Embarassed
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David Bryant



Joined: 29 Jul 2005
Posts: 559
Location: Denver, Colorado

PostPosted: Wed Jul 05, 2006 3:36 pm    Post subject: Why there's a "6" at r7c7. Reply with quote

You guys are making this hint way too complicated. Smile
Code:
+-------------------+-------------------+-------------------+
| 1589  3     589   | 49    149   7     | 2     6     458   |
| 1689  89    4     | 2     5     168   | 189   3     7     |
| 2     5789  56789 | 469   13469 1368  | 14589 1489  458   |
+-------------------+-------------------+-------------------+
| 4     1     78    | 5     2     9     | 3     78    6     |
| 3     6     89    | 1     7     4     | 89    5     2     |
| 59    579   2     | 8     36    36    | 49    479   1     |
+-------------------+-------------------+-------------------+
| 568   58    3     | 7     146   1256  | 14568 148   9     |
| 7     2     569   | 469   8     156   | 1456  14    3     |
| 5689  4     1     | 3     69    56    | 7     2     58    |
+-------------------+-------------------+-------------------+

In this position there's an X-Wing on "6" in columns 3 & 4, rows 3 & 8. Since there are only two ways to enter "6" in columns 3 & 4, there ie either a "6" at r3c3 and a "6" at r8c4, or else there's a "6" at r8c3 & a "6" at r3c4. So you can eliminate "6" from r3c5, r3c6, r8c6, and r8c7.

After this step the "6" at r7c7 is seen to be unique in column 7. dcb
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TKiel



Joined: 22 Feb 2006
Posts: 292
Location: Kalamazoo, MI

PostPosted: Thu Jul 06, 2006 9:50 pm    Post subject: Reply with quote

David Bryant wrote:
You guys are making this hint way too complicated. Smile


I didn't mean to, it's just that I must have been swimming and you and Keith must have been cruising around in the space shuttle when we each did the puzzle.

Keith wrote:
Every waking moment? You've never dreamt about these stupid puzzles? I have! Embarassed


I noticed the time on your post, Keith. Didn't your mom ever tell you about watching scary things just before bed?
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Glassman



Joined: 21 Oct 2005
Posts: 50
Location: England

PostPosted: Fri Jul 14, 2006 11:01 am    Post subject: Reply with quote

TKiel wrote:
... A swordfish is the same concept as an x-wing except it occurs in three rows and 3 columns and can have up to three cells that can contain the digit. There is also a deep-sea creature for 4-4-4 (jellyfish) and 5-5-5 (either starfish or squirmbag). It's not so hard to keep track of once you decide to devote every waking moment to it.

Thanks. It was only recently I found out that what I had been calling boxes and chains were X-wings and their variants.

On a complicated puzzle, I find them by filling in the possibilities for each digit on a separate blank grid, so I have nine 9x9 grids on a piece of paper. Boxes and chains then leap out at you. I've been calling the unfortunate possibilities that you eliminate this way waifs; the easier eliminations that come earlier in puzzle solving strays. Of course, waifs and strays end up in Room 101 for recycling, usually into French accented characters, but for a short time at the moment into Tsarist Russian cyrillic. Room 101 is also the pet name of my compost bin!

Glassman Cool
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TKiel



Joined: 22 Feb 2006
Posts: 292
Location: Kalamazoo, MI

PostPosted: Sat Jul 15, 2006 12:20 pm    Post subject: Reply with quote

Glassman wrote:
On a complicated puzzle, I find them by filling in the possibilities for each digit on a separate blank grid, so I have nine 9x9 grids on a piece of paper.


There are many free, downloadable Sudoku programs that will do that stuff for you. (The one I use is available here) It does confine you to doing the puzzles while at the computer but does cut down on the recycling tonnage. Also keeps the computer area a bit tidier.
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Glassman



Joined: 21 Oct 2005
Posts: 50
Location: England

PostPosted: Sun Jul 16, 2006 4:00 am    Post subject: Reply with quote

TKiel wrote:
... It does ... cut down on the recycling tonnage. ...

I don't buy new paper due to a local initiative trusted small businesses collect low security rated scrap paper and re-use it. It only goes for recycling when it has been used both sides. We've already cut down on the recycling tonnage, and increased the percentage recycled. Most of my file copies are on the back of old property sale information sheets; letters on guillotined down redundant headed letter paper.

Glassman Cool
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