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March 4, '09, hard

 
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Zoelly



Joined: 15 Mar 2009
Posts: 8

PostPosted: Sun Mar 15, 2009 5:31 am    Post subject: March 4, '09, hard Reply with quote

Does this puzzle require any solution techniques beyond the basics: finding pairs, hidden pairs, box-line reduction, or row claiming?
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wapati



Joined: 10 Jun 2008
Posts: 472
Location: Brampton, Ontario, Canada.

PostPosted: Sun Mar 15, 2009 5:39 am    Post subject: Reply with quote

Code:
8 . .|3 7 .|. 4 .
. 6 .|. . 1|. . .
. . 9|. 6 .|. . 2
-----+-----+-----
4 . .|. 5 2|. . 8
2 . .|. . .|. . 7
7 . .|6 9 .|. . 1
-----+-----+-----
9 . .|. 3 .|5 . .
. . .|5 . .|. 1 .
. 8 .|. 4 7|. . 3


No tricks.
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Zoelly



Joined: 15 Mar 2009
Posts: 8

PostPosted: Sun Mar 15, 2009 5:25 pm    Post subject: March 4, '09, hard Reply with quote

thanks!
i'll keep studying the numbers
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storm_norm



Joined: 18 Oct 2007
Posts: 1741

PostPosted: Sun Mar 15, 2009 6:51 pm    Post subject: Reply with quote

the answer to that question is yes !!

there is a hidden pair in this puzzle that I believe you need to find.
as well as a couple intersections
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Zoelly



Joined: 15 Mar 2009
Posts: 8

PostPosted: Tue Mar 17, 2009 3:48 am    Post subject: March 4, '09, hard Reply with quote

I think you might be right, Norm.
Hidden pairs can be so hard to find.
I don't know the term "intersection."

So far I've done FOUR Box-Line Reductions in this puzzle.
1) In Box 1 because of numbers required in Row 1.
2) In Box 3 because of numbers required in Col 9.
3) In Box 7 because of numbers required in Col 1.
4) In Box 9 because of numbers required in Col 9.

Naked pair in Col 5.
Naked pair in Col 4. These were easy.

There was "row claiming" in Box 9 - Row 9.

There was a hidden pair in Box 9.

With all that I've only solved four squares. It's making me cross-eyed!
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Marty R.



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

PostPosted: Tue Mar 17, 2009 4:03 am    Post subject: Reply with quote

Quote:
Hidden pairs can be so hard to find.

Very hard indeed. I've never found a hidden pair, per se. However, for a hidden pair, there is a complementary naked pair, triple, quad, or whatever. That's what I look for, they're much easier for me to find. Give it a try, maybe they'll be easier for you too.

By the way, if you have your intermediate position on the computer, why not post it so some specifics can be pointed out.

Good luck.
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Zoelly



Joined: 15 Mar 2009
Posts: 8

PostPosted: Wed Mar 18, 2009 4:54 am    Post subject: March 4, '09, hard Reply with quote

8 . . |3 7.|. 4 .
. 6 4|. . 1|. . .
. 7 9|. 6 .|. . 2
-----+----+-----
4 . .|7 5 2|. . 8
2 . .|. 1 . |. . 7
7 . .|6 9 .|. . 1
----+---- +-----
9 . .|. 3 .|5 . .
. . . |5 . .|. 1 .
. 8 .|. 4 7|. . 3

This is my current status.[/b]
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Marty R.



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

PostPosted: Wed Mar 18, 2009 5:14 am    Post subject: Reply with quote

Code:

+--------------+------------+------------------+
| 8   125 125  | 3   7  59  | 169    4     569 |
| 35  6   4    | 289 28 1   | 3789   35789 59  |
| 135 7   9    | 48  6  458 | 138    358   2   |
+--------------+------------+------------------+
| 4   139 136  | 7   5  2   | 369    369   8   |
| 2   359 3568 | 48  1  348 | 3469   3569  7   |
| 7   35  358  | 6   9  348 | 234    235   1   |
+--------------+------------+------------------+
| 9   124 1267 | 128 3  68  | 5      2678  46  |
| 36  234 2367 | 5   28 689 | 246789 1     469 |
| 156 8   1256 | 129 4  7   | 269    269   3   |
+--------------+------------+------------------+

Play this puzzle online at the Daily Sudoku site
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storm_norm



Joined: 18 Oct 2007
Posts: 1741

PostPosted: Wed Mar 18, 2009 6:13 am    Post subject: Reply with quote

in the state of the puzzle posted by marty, it is possible to make it through without hidden pairs.
although there is one present in box 9 as it is.


marty,
do you see the hidden pair in box 9?

whenever my eyes find a candidate that only exists twice in a box row or column, then I look for partner candidate that also exists only twice in those same cells.
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nataraj



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

PostPosted: Wed Mar 18, 2009 6:42 am    Post subject: Reply with quote

A starting point would be the naked pair 48 in col 4
Plus: "3" in box 1, "5" in box 6 and "6" in box 4.

The hidden pair 78 in box 9 is a toughie (I never find hidden pairs anyway - sometimes not even hidden singles, shame, but the complementary naked quad 2469 is not too obvious, either Sad )

oops, cross post. didnt see norm's diagram.
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storm_norm



Joined: 18 Oct 2007
Posts: 1741

PostPosted: Wed Mar 18, 2009 6:53 am    Post subject: Reply with quote

Quote:
the complementary naked quad 2469 is not too obvious, either

right,
it might be something one gets a feel for spotting.
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Marty R.



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

PostPosted: Wed Mar 18, 2009 3:47 pm    Post subject: Reply with quote

Quote:
marty,
do you see the hidden pair in box 9?

Norm,

I didn't play the puzzle. I just took the grid Noelly posted and used Nataraj's format tool and added pencil marks in the hope that it would be easier for folks to help out.
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storm_norm



Joined: 18 Oct 2007
Posts: 1741

PostPosted: Wed Mar 18, 2009 4:54 pm    Post subject: Reply with quote

Marty,
since you claim to have never found a hidden pair, the diagram gives you a chance to see one.
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Marty R.



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

PostPosted: Wed Mar 18, 2009 5:31 pm    Post subject: Reply with quote

storm_norm wrote:
Marty,
since you claim to have never found a hidden pair, the diagram gives you a chance to see one.

I'd never see it--and don't think I'd have a need to--because I look for subsets, in this case, an easy 2469 quad. I have no problem with hidden pairs; they just don't work for me. Smile
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Zoelly



Joined: 15 Mar 2009
Posts: 8

PostPosted: Thu Mar 19, 2009 2:40 am    Post subject: Reply with quote

Hi Ho!
I've solved the puzzle!

Thanks to Nataraj, especially, for telling me to look at 3's in box 1. There were so many 3's scattered about in this puzzle that I must have just started to ignore them.

This was one nicely constructed puzzle!

As I noted earlier,"There was a hidden pair in Box 9," I had already found the hidden pair 78.

What I want to know, Marty, is how to distinguish which boxes are making up the naked quad 2469.

Norm, I must honestly admit that I have no clue what all those 8's highlighted in red are showing me. I'm sure it's useful knowledge.

Zoelly
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Zoelly



Joined: 15 Mar 2009
Posts: 8

PostPosted: Thu Mar 19, 2009 2:52 am    Post subject: March 4, '09, hard Reply with quote

Norm,
Well, I kinda do know about all the red 8's, I think!

Is that to show you're eyeballing them --- because you're working on the theory that they're part of a hidden pair?
Green 7's, the same?

Some 8's are highlighted, some are not. On purpose or accidental?
Zoelly
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Marty R.



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

PostPosted: Thu Mar 19, 2009 4:42 am    Post subject: Reply with quote

Quote:
What I want to know, Marty, is how to distinguish which boxes are making up the naked quad 2469.

A naked quad (or quint or triple or pair) has to be in one house, a house being either a row, column or box. In this case, since the hidden pair is in box 9, so is the complementing quad, in cells r7c9, r8c9, r9c7 and r9c8. As I mentioned, I find those infinitely easier to spot than hidden pairs.
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Zoelly



Joined: 15 Mar 2009
Posts: 8

PostPosted: Fri Mar 20, 2009 2:19 am    Post subject: March 4, '09, hard Reply with quote

When naked quads are made of subsets like those seen in box 9, I don't spot them easily. I'm glad you pointed them out for me, Marty.

It's that the 4 appears in only two squares and the 2 appears in only two squares. I wouldn't think to associate them right off. But I do see that they are all subsets of 2469. Tricky!

I'll need more practice to look for them. So in the center box of this puzzle, Box 5, 1348 constitutes an example of naked quads? (Although it doesn't help to solve anything.) If I can begin to recognize them, it's a start.

Zoelly
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