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Saturday, June 10 v. hard

 
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keith



Joined: 19 Sep 2005
Posts: 3136
Location: near Detroit, Michigan, USA

PostPosted: Sat Jun 10, 2006 11:30 pm    Post subject: Saturday, June 10 v. hard Reply with quote

Sam's got us this time!

So far as I can see, the only (reasonable) way to solve this one is with a difficult to spot X-wing. No Unique Rectangles here!

Keith
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Marty R.



Joined: 12 Feb 2006
Posts: 5063
Location: Rochester, NY, USA

PostPosted: Sun Jun 11, 2006 5:38 am    Post subject: Reply with quote

Quote:
So far as I can see, the only (reasonable) way to solve this one is with a difficult to spot X-wing.


I don't know if my way was reasonable or not, but after the basic stuff, I was looking at a rectangle, a Type 3, I believe, but not one that could be solved directly with basic rectangle logic.

However, in the same box as the two corners, there was a third cell containing only the two deadly candidates. I started a chain with the lower number first, and that solved the entire puzzle.
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ulysses



Joined: 30 Jul 2005
Posts: 3

PostPosted: Sun Jun 11, 2006 1:23 pm    Post subject: Reply with quote

What's puzzling me about this sudoku is that it appears to have two solutions. I can get the given solution but equally I can get the following solution:
594712638/768953214/123468795
472689531/386125479/951374862
815237946/639541827/247896153

These are all rows starting at the top and working downwards.

I got to a point where there was a subset of numbers that appeared to be self contained. I took a square with only 2 possible solutions and tried each in turn. Once produced the given solution and the other produced the above solution. I can see nothing wrong with it.

I should also say I'm in the habit of missing obvious errors so I would be grateful (if there is an error) if someone could point it out to me!
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jabejochke



Joined: 16 Mar 2006
Posts: 21
Location: Reading

PostPosted: Sun Jun 11, 2006 2:02 pm    Post subject: Reply with quote

Code:

5      9    2348   7       12     24    6         1238   28   
17    6    28       9       5       3     278      128     4   
17    24   234    46      126   8      237     9         5   
234  7     246    346    8       9      5        23       1
234  8     246    1        26     5      234    7         9
9     5     1        34      7       24    2348   6        28
8     1     5        2        3       7     9         4        6
6     3     9        5        4       1     28       28       7
24   24   7        8        9       6     1          5        3           



This is point I reached when I started looking for x-wings, unique rectangles etc.

Found the x-wing of 2's at R16C69 and a rectangle at R28C78. Took the X-wing path and went to solution; however, could not do anything with the unique rectangle. Can the solution be gotten using the UR as the starting point.

Appreciate any insights.

Thanks,

Jabejochke

PS Please excuse the wiggly picture -- I haven't figured out how to use the Code: function.
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ulysses



Joined: 30 Jul 2005
Posts: 3

PostPosted: Sun Jun 11, 2006 3:13 pm    Post subject: Reply with quote

That's the point I got to. I found if I entered 4 in the extreme bottom left square, I got the given answer. However, if I entered 2 (other other possibility) I got the alternative solution I posted, which also appears to be OK.
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Marty R.



Joined: 12 Feb 2006
Posts: 5063
Location: Rochester, NY, USA

PostPosted: Sun Jun 11, 2006 4:05 pm    Post subject: Reply with quote

Code:

5     9    2348   7       12     24    6        1238   28   
17    6    28     9       5      3     278      128    4   
17    24   234    46      126    8     237      9      5   
234   7    246    346     8      9     5        23     1
234   8    246    134     7      24    2348     6      28
8     1    5      2       3      7     9        4      6
6     3    9      5       4      1     28       28     7
24    24   7      8       9      6     1        5      3   


Quote:
Found the x-wing of 2's at R16C69 and a rectangle at R28C78. Took the X-wing path and went to solution; however, could not do anything with the unique rectangle. Can the solution be gotten using the UR as the starting point.


Yes and no. I don't believe anything can be done directly with the UR, but with r1c9 containing the 28, that's a good opportunity for starting a forcing chain. That's what I did and the "2" solved the puzzle.

Quote:
PS Please excuse the wiggly picture -- I haven't figured out how to use the Code: function.


As recommended to me here, I type my grids in Notepad, but it should work OK here too. The key is having the same number of characters, including spaces, for every cell. Look at the cell with the most candidates and add one or two. In this case four is the most candidates in a cell, so I add one, thus every cell will have five characters. If the cell is solved, I type four spaces after the single digit. If it has two candidates, type three spaces, and so on such that the the number of candidates plus spaces equals five, in this case. I copied your grid to Notepad and it took about one minute to align it via typing spaces and/or backspacing.
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keith



Joined: 19 Sep 2005
Posts: 3136
Location: near Detroit, Michigan, USA

PostPosted: Sun Jun 11, 2006 4:10 pm    Post subject: Invalid solution! Reply with quote

You posted:
Code:

594712638
768953214
123468795
472689531
386125479
951374862
815237946
639541827
247896153

which has two 8's in C7, and two 3's in C8.

Keith
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ulysses



Joined: 30 Jul 2005
Posts: 3

PostPosted: Sun Jun 11, 2006 4:45 pm    Post subject: Reply with quote

Many thanks. As I said, I have a tendency to make errors which are obvious once they are pointed out!
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gf1701



Joined: 27 May 2006
Posts: 4

PostPosted: Wed Jun 14, 2006 6:26 am    Post subject: Reply with quote

I've read these postings but I don't understand the language. What is an X-wing? What is a deadly candidate? What does the notation R16C69 refer to (obviously not Row 16, Column 69!)?

Gary

P.S. When I tried the Hint feature on this puzzle, at the point I'd reached, nothing happened; first time I've seen that.
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keith



Joined: 19 Sep 2005
Posts: 3136
Location: near Detroit, Michigan, USA

PostPosted: Wed Jun 14, 2006 9:41 am    Post subject: Reply with quote

Gary,

Start here:

http://www.sudoku.com/forums/viewtopic.php?p=21804#21804

Keith
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gf1701



Joined: 27 May 2006
Posts: 4

PostPosted: Mon Jun 19, 2006 3:27 am    Post subject: Reply with quote

Thanks for the links. I think http://angusj.com/sudoku/hints.php is the best place to go for an explanation of terms. But I still don't know what R16C69 and R28C78 refer to. Without that information, I can't interpret the posting above that points to the puzzle's solution.
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Marty R.



Joined: 12 Feb 2006
Posts: 5063
Location: Rochester, NY, USA

PostPosted: Mon Jun 19, 2006 5:04 am    Post subject: Reply with quote

Quote:
But I still don't know what R16C69 and R28C78 refer to.


R16C69 = rows 1 and 6, columns 6 and 9.

R28C78 = rows 2 and 8, columns 7 and 8.
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