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May 26th Hard Puzzle

 
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eddieg



Joined: 12 Jan 2006
Posts: 47
Location: San Diego, CA USA

PostPosted: Fri May 26, 2006 3:14 pm    Post subject: May 26th Hard Puzzle Reply with quote

A little "Help!" required - Here's where I am at.

000 507 006
000 064 070
076 002 040

465 981 327
030 756 010
197 423 568

610 240 700
000 370 601
750 618 000

The hint is for a 4 in R1C2.

From doing my sweeps I know that R1C2 or R1C3 needs to be a 4. I also see that my only possibilities for a 4 in column 2 are in rows 1 and 8. I just don't see how the possibilities of 2 and 8 being eliminated in R1C2 give me the result of 4 in this particular cell.

Thanks in advance for any help.
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David Bryant



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

PostPosted: Fri May 26, 2006 3:52 pm    Post subject: Follow the pairs ... Reply with quote

Hi, eddieg!

-- The "8" in column 8 must appear in the bottom right 3x3 box.

-- Therefore the only possibilities at r1c8 are {3, 9}. This pairs up with the {3, 9} in r1c5, so the values {3, 9} can be eliminated in the rest of row 1.

-- Look at the top left 3x3 box. The possibilities at r1c1 are {2, 3, 8, 9}. At r1c2 they're (2, 4, 8}, and at r2c2 they're {2, 8}. But when you eliminate the {3, 9} at r1c1 you'll see the {2, 8} pair in r1c1 & r2c2, leaving "4" as the only possibility at r1c2.

-- There's also a {2, 8} in r5c1. So once you've identified the {2, 8} at r1c1 you'll have a pair in column 1, from which you can set r8c1 = 9. This is what I actually saw when I hit this spot in the puzzle this morning -- I didn't notice the {2, 8} at r2c2 until a little later. dcb
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eddieg



Joined: 12 Jan 2006
Posts: 47
Location: San Diego, CA USA

PostPosted: Fri May 26, 2006 4:12 pm    Post subject: Reply with quote

Thanks again.

I was reading "to much" into the "28" pairs in that area of the puzzle, and was thinking that there was some more "advanced" technique involved.
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fkhalili2002



Joined: 28 May 2006
Posts: 6

PostPosted: Sun May 28, 2006 5:16 pm    Post subject: Need help with the 05/26/06 Hard Soudoku Reply with quote

Hello Guys, I am kind of a newby with Sudoku but I'm doing alright so far. I just need a little help as I am just one step behind eddieg when he posted the original request for help.

Here is where I am:
000 507 006
000 064 070
076 002 040

465 981 327
030 756 010
197 423 568

610 240 700
000 370 601
700 618 000

I don't see the logic about how "5" ends up in R9C2 and it's driving me nuts. Would you please explain the reasoning?

Thanks.
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Marty R.



Joined: 12 Feb 2006
Posts: 5175
Location: Rochester, NY, USA

PostPosted: Sun May 28, 2006 5:55 pm    Post subject: Reply with quote

Quote:
I don't see the logic about how "5" ends up in R9C2 and it's driving me nuts. Would you please explain the reasoning?

I don't know what you're looking at and I do puzzles strictly with pencil and paper and eraser. After filling in cells with their candidates and doing a few eliminations, rows 8 and 9 looked like this:

Code:
|2589  |2458  2489  |3     7     59    |6     589   1     |   
|7     |245   2349  |6     1     8     |249   359   23459 |


Note that in row 8 the only possibilities for 2 and 4 are in box 7. Therefore, 2 and 4 must be eliminated from rows 7 and 9 in box 7. When these are removed from r9c2, only the 5 is left standing.

Hope this helps return you to sanity. Smile
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David Bryant



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

PostPosted: Sun May 28, 2006 5:57 pm    Post subject: Row on block interactions Reply with quote

Hi, fkh! Welcome to the forum.

This is a case of "row on 3x3 block interaction."

-- Observe, first, that there are 5 open cells in row 8. Three of these lie in the bottom left 3x3 box, and only two lie outside that box (r8c6 & r8c8).

-- Notice next that neither "2" nor "4" can lie in r8c6 or r8c8. So both the "2" and the "4" in row 8 must lie in the bottom left 3x3 box.

-- Now think about the apparent possibilities at r9c2. It looks as if it could be {2, 4, 5}. But it can't be "2" or "4", because those have to lie in row 8 in this box, by our reasoning above. So the only value left is "5". dcb
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fkhalili2002



Joined: 28 May 2006
Posts: 6

PostPosted: Sun May 28, 2006 6:55 pm    Post subject: May 26th Hard Puzzle Reply with quote

Thank you Marty R. and David Bryant for your help Very Happy . I now see the light and how you got there Embarassed . And yes Marty, it restored my sanity (at least temporarily) until I get to the next tough one and there will be a lot of tough ones while I am learning the techniques and thought processes that are probably as easy as drinking water for your guys.

Thanks again and hopefully I won't bother you any more for this puzzle. fkh
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Marty R.



Joined: 12 Feb 2006
Posts: 5175
Location: Rochester, NY, USA

PostPosted: Sun May 28, 2006 9:32 pm    Post subject: Re: May 26th Hard Puzzle Reply with quote

fkhalili2002 wrote:
Thank you Marty R. and David Bryant for your help Very Happy . I now see the light and how you got there Embarassed . And yes Marty, it restored my sanity (at least temporarily) until I get to the next tough one and there will be a lot of tough ones while I am learning the techniques and thought processes that are probably as easy as drinking water for your guys.

Thanks again and hopefully I won't bother you any more for this puzzle. fkh


Heh, heh, lumping David and me together is not exactly an accurate observation. He has a Sudoku PhD and I'm still working on my BA.

I've been at it for about six months now. I scoured a bunch of web sites, learning techniques wherever I could. Then I joined this forum over three months ago and have been asking questions ever since. David is one of those who have been immensely generous and helpful.

The web sites were very good at teaching me basic techniques, but most of the so-called "advanced" techniques that I can use are because they were explained to me right here.

After taking so much from this forum, I'm delighted to be able to occasionally give something back by helping someone who is newer at it than I am. Very Happy
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sdtibbs



Joined: 08 May 2006
Posts: 6

PostPosted: Sun May 28, 2006 9:42 pm    Post subject: Reply with quote

I am confused with the explanation of the May 26th puzzle. I do not see how there is not an option of a 5 in r2c1 or r3c1. It was stated that the possibilities of r1c1 were 2,3,8,9, and there was not an option of 5. I find that the only place a 5 can go is in either r2c1 or r3c1. I solved the problem with the 5 in r3c1. Please help. :?
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fkhalili2002



Joined: 28 May 2006
Posts: 6

PostPosted: Mon May 29, 2006 5:31 am    Post subject: May 26th Hard Puzzle Reply with quote

I am sorry SDT, maybe I am missing something. You said that "it was stated that the possibilities of r1c1 were 2,3,8,9 and there was not an option for 5". This is a true statement stated by David Bryant, as r1c4 contains a "5". However, if you really meant r2c1 or r3c1, I don't believe anyone has said these cells can not have a "5". In fact running sweeps shows the possibility of having "5" in these cells, and your assessment and solution is correct. Hope this helps, if not please let me know. fkh
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sdtibbs



Joined: 08 May 2006
Posts: 6

PostPosted: Mon May 29, 2006 8:55 pm    Post subject: Reply with quote

Thanks for getting me straight. Had my r and c wrong; had been working on the puzzle for awhile and got cross-eyed. thanks again. Very Happy
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