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David Bryant
Joined: 29 Jul 2005
Posts: 559
Location: Denver, Colorado
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 Posted: Mon Oct 03, 2005 8:11 pm Post subject: A very tough minimal sudoku |
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I've been working through some of the 17-clue Sudokus, just for practice. Interestingly, most of the 17-clue Sudokus I've tried so far are fairly easy to solve. But some of them aren't so simple. Here's a very hard one.
| Code: |
. . . 9 . . 8 4 .
5 . 1 . . . . . .
3 . . . . . . 9 .
. 4 . 2 . . 5 . .
. . . 7 6 . . . .
. . . . . . 3 . .
. . . . 3 1 . . .
. 6 . . . . . . 7
. . . . . . . . .
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I didn't have to use any "advanced techniques" to get most of the way through this puzzle. I found it difficult during the early going because it wasn't easy to spot the next number that could be placed in the grid. After 52 moves (12 spots left open) I reached a position that wasn't easily resolved -- but since there were only a few moves left at that point, brute force was enough to find the (unique) solution.
In case anyone else is interested in these "minimal" Sudoku puzzles, you can find a great number of them at http://www.csse.uwa.edu.au/~gordon/sudokumin.php. This one is #7768 from that collection. (Thanks to Someone_Somewhere for pointing this site out in an earlier post). dcb |
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someone_somewhere
Joined: 07 Aug 2005
Posts: 275
Location: Munich
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| Posted: Tue Oct 04, 2005 9:25 am Post subject: |
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Hi David,
No need for brute force, an XY-wing is solving it.
Tip:
2 not in r7c8, XY-Wing-1 X=8 Y=9 in r5c1 X=8 Z=2 in r5c8 Y=9 Z=2 in r7c1
hope it fits the point you got stacked. If not I can supply you my solution.
see u, |
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David Bryant
Joined: 29 Jul 2005
Posts: 559
Location: Denver, Colorado
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| Posted: Tue Oct 04, 2005 11:57 am Post subject: |
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| You're right -- that is the spot where I was stuck. I don't really know how to spot those "XY-Wing" combinations yet ... I guess I need more practice. dcb |
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someone_somewhere
Joined: 07 Aug 2005
Posts: 275
Location: Munich
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| Posted: Wed Oct 05, 2005 7:13 am Post subject: |
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Hi David,
You want a couple of Sudoku that can be solved with XY-wing?
see u, |
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David Bryant
Joined: 29 Jul 2005
Posts: 559
Location: Denver, Colorado
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| Posted: Thu Oct 06, 2005 10:33 pm Post subject: |
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| someone_somewhere wrote: | Hi David,
You want a couple of Sudoku that can be solved with XY-wing?
see u, |
Yes, please -- I'd like some more "XY-Wing" examples. You can send me e-mail at davidbryant@att.net, or post a private message through this forum.
Thanks! dcb |
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Guest
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| Posted: Fri Oct 07, 2005 4:21 pm Post subject: Some Sudoku that need XY-wing tehcnique |
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Hi,
Here one that needs XY-wing technique:
000010780
500009000
000000040
026000000
000600003
074080000
000003002
080040010
600500000
You will have to use some tehcniques like:
Row on 3x3 Block interaction
Column on 3x3 Block interaction
3x3 Block on Row/Column
Hidden Pair in Row
in Column
in 3x3 Block
Nacked Pair on Row
and of course:
XY-wing
The above ones are sufficient.
good look!
see u, |
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Guest
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| Posted: Fri Oct 07, 2005 4:25 pm Post subject: |
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Hi,
An other one that needs XY-wing:
000010780
500009000
000000040
026000000
000600003
074080000
000003002
080040010
600500000
see u, |
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Guest
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| Posted: Fri Oct 07, 2005 4:28 pm Post subject: |
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Hi,
one more:
014050000
000006008
002000000
000800002
005010900
600007000
000000100
700300000
000090540
see u, |
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Guest
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| Posted: Fri Oct 07, 2005 4:30 pm Post subject: |
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Hi,
This one is a "Leckerbissen". You will need X-wing and XY-wing.
010007030
000005000
062010840
370800000
008060200
000001089
089020350
000400000
050300060
see u, |
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Guest
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| Posted: Fri Oct 07, 2005 4:33 pm Post subject: |
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Hi,
Now it should not be a problem to find the XY-wing from this one:
900500362
253900810
601203950
069032085
100608039
300490076
530004698
890300741
010809523
see u, |
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Guest
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| Posted: Fri Oct 07, 2005 4:37 pm Post subject: |
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Hi,
From this one:
020000000
000600003
074080000
000003002
080040010
600500000
000010780
500009000
000000040
you can eliminate 5 numbers using XY-wing.
see u, |
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Guest
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| Posted: Fri Oct 07, 2005 4:40 pm Post subject: |
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Hi,
In this one I could find also 1 XY-wing:
000000021
500040000
000000070
000300600
000020500
010000000
600000203
003107000
000008000
see u, |
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Guest
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| Posted: Fri Oct 07, 2005 4:42 pm Post subject: |
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Hi,
I got stucked after finding 33 numbers with this one:
400000001
080400000
000000000
000700850
001900000
200000000
030006080
600010400
XY-wing solved it.
see u, |
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Guest
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| Posted: Fri Oct 07, 2005 4:46 pm Post subject: |
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Ok, one with hidden pair, X-wing and XY-wing:
500000000
400070006
908405000
010003090
005209600
040800020
000604503
700020004
000000009
By now, the coffee should be still hot after you have solved it!
see u, |
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Guest
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| Posted: Fri Oct 07, 2005 4:52 pm Post subject: XY-wing of two kinds: on column and/or on row |
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Hi,
By now you should have found out that there are two kind of XY-wing:
on row and/or on column.
Hope that now we have enough example posted.
There is only one thing left: to find them!
good look & see u, |
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David Bryant
Joined: 29 Jul 2005
Posts: 559
Location: Denver, Colorado
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| Posted: Fri Oct 07, 2005 11:19 pm Post subject: Re: Some Sudoku that need XY-wing tehcnique |
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| Someone_Somewhere wrote: | Hi,
Here one that needs XY-wing technique:
000010780
500009000
...
see u, |
Thanks for all the examples. Since this topic is getting sort of long, I'm going to start a new topic, "XY-Wing Example #1," to discuss this puzzle.
Just for the record, I didn't have to use "XY-Wing" to solve this puzzle. But the first move was pretty hard to find ... after that it went fairly quickly. dcb |
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