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April 26 VH - One trick wonder
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prakash



Joined: 02 Jan 2008
Posts: 67
Location: New Jersey, USA

PostPosted: Sat Apr 26, 2008 12:27 am    Post subject: April 26 VH - One trick wonder Reply with quote

After the basics
Code:

+-----------+-------------+-----------+
| 1  34  9  | 34  58  7   | 68 56 2   |
| 7  6   58 | 158 2   158 | 4  9  3   |
| 38 345 2  | 34  9   6   | 7  1  58  |
+-----------+-------------+-----------+
| 5  9   1  | 2   7   4   | 3  8  6   |
| 2  7   36 | 568 58  358 | 9  4  1   |
| 4  8   36 | 9   16  13  | 5  2  7   |
+-----------+-------------+-----------+
| 9  1   58 | 7   46  2   | 68 3  458 |
| 6  2   4  | 58  3   58  | 1  7  9   |
| 38 35  7  | 16  146 9   | 2  56 458 |
+-----------+-------------+-----------+


Just crack the XY-Wing 58-68-56 and everything falls in place.
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storm_norm



Joined: 18 Oct 2007
Posts: 1741

PostPosted: Sat Apr 26, 2008 1:20 am    Post subject: Reply with quote

UR {3,4}
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tlanglet



Joined: 17 Oct 2007
Posts: 2468
Location: Northern California Foothills

PostPosted: Sat Apr 26, 2008 1:47 am    Post subject: Reply with quote

How do you do it? I am in California, USA and it is now about 6:40 PM. I accessed today's puzzle but I got what I expected: the puzzle for Friday, April 25th. BUT, Prakash, living in New Jersey, USA, has already posted the puzzle for Saturday, April 26th, where the time is 9:40PM on April 24th.

Prakash, will you share the secret?

Ted
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storm_norm



Joined: 18 Oct 2007
Posts: 1741

PostPosted: Sat Apr 26, 2008 4:08 am    Post subject: Reply with quote

Ted,

one word hint

"syndication"

on the home page, click on syndication about 5 or 6 pm cali time.

I live in pennsylvania and I usually look around 8 or 9 after London goes past midnight because the puzzle has to be posted under the syndication link in order for the rest of the earth to syndicate it.
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crunched



Joined: 05 Feb 2008
Posts: 168

PostPosted: Sat Apr 26, 2008 4:50 am    Post subject: Reply with quote

Or you can simply click your computer's clock and change your time zone (example: london is 6 hrs ahead of central time).
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tlanglet



Joined: 17 Oct 2007
Posts: 2468
Location: Northern California Foothills

PostPosted: Sat Apr 26, 2008 7:04 am    Post subject: Reply with quote

As always, thanks for the help. Surprised

Ted
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nataraj



Joined: 03 Aug 2007
Posts: 1048
Location: near Vienna, Austria

PostPosted: Sat Apr 26, 2008 9:55 am    Post subject: Reply with quote

I used a w-wing 58-(38-38)-58.

One of those wimpy VHs.
(edited to disable smiley)


Last edited by nataraj on Sat Apr 26, 2008 4:52 pm; edited 1 time in total
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cgordon



Joined: 04 May 2007
Posts: 769
Location: ontario, canada

PostPosted: Sat Apr 26, 2008 11:54 am    Post subject: Reply with quote

That's interesting: We can knock off the <5> in R9C2 using three different techniques.
1) A Type 2 UR <345> in R12C24.
2) An x-wing <568>
3) An ER using <5> in Box 9 and R3.
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Clement



Joined: 24 Apr 2006
Posts: 1111
Location: Dar es Salaam Tanzania

PostPosted: Sat Apr 26, 2008 6:44 pm    Post subject: Daily Sudoku: Sat 26-Apr-2008 VH Reply with quote

XY-Wing pivot at {6,8}r7c7 with pincers{5,8}r7c3 and {5,6}r9c8 eliminating 5 in r9c2. This solves the puzzle.
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keith



Joined: 19 Sep 2005
Posts: 3355
Location: near Detroit, Michigan, USA

PostPosted: Sat Apr 26, 2008 7:03 pm    Post subject: Reply with quote

tlanglet wrote:
How do you do it? I am in California, USA and it is now about 6:40 PM. I accessed today's puzzle but I got what I expected: the puzzle for Friday, April 25th. BUT, Prakash, living in New Jersey, USA, has already posted the puzzle for Saturday, April 26th, where the time is 9:40PM on April 24th.

Prakash, will you share the secret?

Ted

Tomorrow's puzzle is a Medium with <856> in R123C1.

Go look at the printable puzzle, and change the date in the URL:

http://www.dailysudoku.com/sudoku//pdf/2008/04/2008-04-26_S2_N1.pdf

http://www.dailysudoku.com/sudoku//pdf/2008/04/2008-04-27_S2_N1.pdf

The "syndication" puzzle is still today's. (It is 3 pm EDT.)

Keith
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Clement



Joined: 24 Apr 2006
Posts: 1111
Location: Dar es Salaam Tanzania

PostPosted: Sat Apr 26, 2008 8:12 pm    Post subject: Daily Sudoku: Sat 26-Apr-2008 VH Reply with quote

XY-Wing pivot 6,8}r7c7 with pincers {5,8}r7c3 and {5,6}r9c8 eliminating 5 in r9c2. This solves the puzzle.
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Clement



Joined: 24 Apr 2006
Posts: 1111
Location: Dar es Salaam Tanzania

PostPosted: Sat Apr 26, 2008 8:36 pm    Post subject: Daily Sudoku: Sat 26-Apr-2008 VH Reply with quote

XY-Wing pivot at {6,8}r7c7 with pincers{5,8}r7c3 and {5,6}r9c8 eliminating 5 in r9c2. This solves the puzzle.
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Dart45



Joined: 16 Apr 2008
Posts: 17
Location: Canada

PostPosted: Sat Apr 26, 2008 11:45 pm    Post subject: Reply with quote

Posted here before my incredulity at the lengths that some people here go to make things complicated. All this talk about pincers, jellyfish, xy-wings and pivots, etc., etc.

This approach just mechanizes the solution process and kills the fun of solving a puzzle!

As usually, I managed to solve the puzzle as it came, without pencil marks or anything else. Just one square at a time!

As I wrote before, the Easy and Medium levels are never a problem, the Hard ones get me every once in a while, and the Very Hard ones are the real challenge - but most satisfying to solve. Todays was no different - a very pleasant and satisfying challenge to solve outright.
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nataraj



Joined: 03 Aug 2007
Posts: 1048
Location: near Vienna, Austria

PostPosted: Sun Apr 27, 2008 7:41 am    Post subject: Reply with quote

Dart45 wrote:
As usually, I managed to solve the puzzle as it came, without pencil marks or anything else. Just one square at a time!


So again, you've let us know how great you are. Thanks, that is valuable information.

Now that I've acknowledged your greatness, Is there maybe something else you would like to talk about?

Like, for example, the subject matter here, i.e. today's sudoku? Or the solution path, maybe? Or how there are different ways to approach difficult points?

In that case I suggest you come up with a little more than "I did it". "I did it again".

Otherwise all I can say is "Wow!". And "Wow again!"
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crunched



Joined: 05 Feb 2008
Posts: 168

PostPosted: Sun Apr 27, 2008 2:41 pm    Post subject: Reply with quote

Dart45 wrote:

This approach just mechanizes the solution process and kills the fun of solving a puzzle!
SNIP
As usual, I managed to solve the puzzle as it came, without pencil marks or anything else. Just one square at a time!



I tend to see that "mechanizing" solutions would take the challenge---and the fun---out of finding solutions to a puzzle. But toiling endlessly without ever finding a solution also takes the fun out of this. By no means do I understand the "fishy" solutions, coloring or some of the other methods. Maybe someday I will get around to learning them.

Without the help of wings or other advanced techniques, I am absolutely incapable of solving some puzzles---even after stewing for 8 hours on a puzzle!
When I find out the reason that a technique works, (for example, how and why the pincers of an xy-wing force the removal of a number), then that is very satisfying to me too.

Kudos to you if you use no techniqes or no shortcut solutions to solve these puzzles. That would never be possible for me. Especially pencil marks! I doubt I could even solve an easy puzzle without using pencil marks to eliminate numbers. For one thing, pencil marks memorialize what I have discovered about a row, column, box and cell. I can't poke all this information in my head and remember it.

So how do you solve these puzzles with sheer brain, memory and concentration power?
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Dart45



Joined: 16 Apr 2008
Posts: 17
Location: Canada

PostPosted: Sun Apr 27, 2008 9:03 pm    Post subject: Reply with quote

First of all, I did not intend to sound like I had a monopoly on brain. My point was that not using any of the “tricks” made it more fun and satisfying to get the solution.

My approach is to make a pass at the entire puzzle, sequentially from 1 through 9, looking for the obvious fills. On the Easy and Medium puzzles, one pass is usually enough to fill 50 to 75% of the squares, and the solution from there is almost trivial. On the Hard and Very Hard, a second pass is required, because the filled squares by higher numbers open new opportunities not seen for the preceding lower numbers. Thereafter I look for rows, columns or blocks with 2, 3 and 4 missing numbers, and try to find fills for as many squares as possible. This usually solves the Hard puzzles. The Very Hard puzzles will require several iterations, and will also require the memorizing of the possible fill options in the process.

My process is a lot like playing chess, analyzing and planning several moves ahead. There are no tricks or pencil-marks in chess. It is just practice, determination, persistence and perseverance.
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keith



Joined: 19 Sep 2005
Posts: 3355
Location: near Detroit, Michigan, USA

PostPosted: Sun Apr 27, 2008 9:48 pm    Post subject: Reply with quote

Dart45 wrote:
First of all, I did not intend to sound like I had a monopoly on brain. My point was that not using any of the “tricks” made it more fun and satisfying to get the solution.

My approach is to make a pass at the entire puzzle, sequentially from 1 through 9, looking for the obvious fills. On the Easy and Medium puzzles, one pass is usually enough to fill 50 to 75% of the squares, and the solution from there is almost trivial. On the Hard and Very Hard, a second pass is required, because the filled squares by higher numbers open new opportunities not seen for the preceding lower numbers. Thereafter I look for rows, columns or blocks with 2, 3 and 4 missing numbers, and try to find fills for as many squares as possible. This usually solves the Hard puzzles. The Very Hard puzzles will require several iterations, and will also require the memorizing of the possible fill options in the process.

My process is a lot like playing chess, analyzing and planning several moves ahead. There are no tricks or pencil-marks in chess. It is just practice, determination, persistence and perseverance.

So, Dart45, at this point, what would you do, and why?
Code:
+-------------+-------------+-------------+
| 1   34  9   | 34  58  7   | 68  56  2   |
| 7   6   58  | 158 2   158 | 4   9   3   |
| 38  345 2   | 34  9   6   | 7   1   58  |
+-------------+-------------+-------------+
| 5   9   1   | 2   7   4   | 3   8   6   |
| 2   7   36  | 568 58  358 | 9   4   1   |
| 4   8   36  | 9   16  13  | 5   2   7   |
+-------------+-------------+-------------+
| 9   1   58  | 7   46  2   | 68  3   458 |
| 6   2   4   | 58  3   58  | 1   7   9   |
| 38  35  7   | 16  146 9   | 2   56  458 |
+-------------+-------------+-------------+

Keith
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DennyOR



Joined: 12 Sep 2007
Posts: 33
Location: Portland, Oregon

PostPosted: Sun Apr 27, 2008 9:50 pm    Post subject: Reply with quote

I solved the puzzle with an 86-65-53-38 xy-chain, which has two cells in common with the 58-86-65 xy-wing solution.
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crunched



Joined: 05 Feb 2008
Posts: 168

PostPosted: Mon Apr 28, 2008 1:19 am    Post subject: Reply with quote

DennyOR wrote:
I solved the puzzle with an 86-65-53-38 xy-chain, which has two cells in common with the 58-86-65 xy-wing solution.


It is interesting that you are using four cells for an xy-wing.
I see how it works. I am rephrasing your numbers to 38-35-56-68, which starts on and runs across row 9 for the first 3 of the pairs. The last pair is 68 in the same box as 56.
It really seems that you should use 38-35-56-68-58 as the string of numbers.

Assuming 38 is a 3, it trips 35 to 5, then 56 to 6 and 68 to 8 and then (58 in row 7 column 3) to 5.

Start over, and assume 38 is an 8, that trips (58 in row 7 column 3) to 5.
Ergo (58 in row 7 column 3) is a 5. Period. 35 is a 3. Period. And on it goes.

BTW, I was able to solve the puzzle with a UR using 34 in the first 2 boxes. It is a lot easier for me to spot a UR than wings.
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Marty R.



Joined: 12 Feb 2006
Posts: 5770
Location: Rochester, NY, USA

PostPosted: Mon Apr 28, 2008 3:56 am    Post subject: Reply with quote

Quote:
It is interesting that you are using four cells for an xy-wing.


He's using a four-cell XY-Chain, not an XY-Wing. Either the start or end of the chain must be = 8, so they act as pincers to kill the 8 in r7c3.
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