dailysudoku.com Forum Index dailysudoku.com
Discussion of Daily Sudoku puzzles
 
 FAQFAQ   SearchSearch   MemberlistMemberlist   UsergroupsUsergroups   RegisterRegister 
 ProfileProfile   Log in to check your private messagesLog in to check your private messages   Log inLog in 

WHERE FROM HERE?

 
Post new topic   Reply to topic    dailysudoku.com Forum Index -> Daily Sudoku puzzles
View previous topic :: View next topic  
Author Message
HOLLYDOLL
Guest





PostPosted: Tue Nov 01, 2005 3:09 pm    Post subject: WHERE FROM HERE? Reply with quote

I AM STUCK AND NEED SOME HELP - I THINK I WILL SOON GET THTESE BUT FOR NOW AM AT A LOSS. THANKS

713 892 XX4
428 657 931
XXX X4X 278

X47 2X8 3XX
8XX 7X5 4X2
XX2 9X4 817

2X9 X8X 74X
X8X 47X X29
674 529 183
Back to top
someone_somewhere



Joined: 07 Aug 2005
Posts: 275
Location: Munich

PostPosted: Tue Nov 01, 2005 3:27 pm    Post subject: Reply with quote

Hi Hollydolly,

XY-wing will do it. Try to look for one.

If you don't spot it, here some help:

5 not in r4c1, it is in r6c1 or r6c2 (Row on 3x3 Block interaction)
1 not in r8c6, it is in r7c4 or r7c6 (same)
9 not in r4c8, XY-Wing-2 X=6 Y=1 in r5c3 X=6 Z=9 in r5c8 Y=1 Z=9 in r4c1
9 in r4c1 9 in r5c8 - Unique Horizontal
...

see u,
Back to top
View user's profile Send private message
HOLLYDOLL
Guest





PostPosted: Tue Nov 01, 2005 8:44 pm    Post subject: STUCK Reply with quote

IF I KNEW WHAT AN XY-WING WAS I WOULD TRY TO FIND IT. COULD YOU LET ME KNOW WHAT ONE IS? IN SIMPLE TERMS PLEASE.
I NEVER HAD A 5 IN R4 C1 - I HAD JUST A 1 AND A 9 - THE RET OF WHAT YOU SAY I DO HAVE. THANKS FOR THE HELP. H
Back to top
someone_somewhere



Joined: 07 Aug 2005
Posts: 275
Location: Munich

PostPosted: Tue Nov 01, 2005 8:50 pm    Post subject: Reply with quote

Hi,

Just get to the "General Discussion" and there you will find a thread
"x-y wing".

After reading it, please feel free to post your question(s) and we will try to help.

see u,
Back to top
View user's profile Send private message
David Bryant



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

PostPosted: Tue Nov 01, 2005 10:15 pm    Post subject: What is an "xy-wing"? Reply with quote

Here, Holly -- I'll help you understand the "xy-wing." Or at least, I will try.

At the point you've reached in the puzzle, there are four critical cells. These are r4c1, r4c8, r5c3, and r5c8. If you analyze these cells carefully you will see that only the following values are possible at these four locations.

r4c1 is either 1 or 9.
r4c8 is either 5, 6, or 9.
r5c3 is either 1 or 6.
r5c8 is either 6 or 9.

Consider what would happen if one were to place a "1" at r5c3. Then r4c1 would be a "9" (in the same 3x3 box) and "9" would be ruled out at r4c8.

What if there's a "6" at r5c3? Then r5c8 would be a "9", and "9" would still be ruled out at r4c8.

Either way, then, there cannot be a "9" at r4c8 -- the only place where a "9" can fit in row 4 is therefore r4c1, and the puzzle can be easily solved from there.

There has been a lot of discussion of the "xy-wing" in the "Other puzzles" section of this forum -- try reading about it here or here or here or here. dcb
Back to top
View user's profile Send private message Send e-mail Visit poster's website
HOLLYDOLL
Guest





PostPosted: Wed Nov 02, 2005 3:12 pm    Post subject: STUCK Reply with quote

DAVID - THANK YOU FOR YOUR HELP. ONE LAST THING I WOULD LIKE TO KNOW: HOW DOES ONE RECOGNIZE THE XY-WING? WHAT WOULD I LOOK FOR?
Back to top
David Bryant



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

PostPosted: Wed Nov 02, 2005 4:14 pm    Post subject: Finding the "XY-Wing" formation Reply with quote

I'm probably the wrong guy to ask, Holly. I still have difficulty locating these.

The "XY-Wing" always involves four cells in the puzzle, and three of these must contain values that fit the general pattern {X, Y}, {X, Z}, {Y, Z}. These three must be logically linked to each other (ie, same row, or column, or box). The fourth cell must have Z as one of its possible values, and it must line up with the {X, Z} and {Y, Z} cells by sharing a row, a column, or a 3x3 box with both.

When I'm stuck and I think the "XY-Wing" might help I concentrate on all the cells that have been reduced to pairs. I just review them one by one, looking to see if I can find neighboring cells that fit the pattern I've described. Sometimes I can find three cells that fit the "XYZ" pattern, but there is no fourth cell that lines up right to get any useful information. On a couple of puzzles I've located the "XY-Wing," but the value I was able to eliminate wasn't really useful for solving the rest of the puzzle.

I think practice is the only medicine for this one, Holly. dcb

PS BTW, you post on this forum quite a lot. When are you going to register? Smile
Back to top
View user's profile Send private message Send e-mail Visit poster's website
Display posts from previous:   
Post new topic   Reply to topic    dailysudoku.com Forum Index -> Daily Sudoku puzzles All times are GMT
Page 1 of 1

 
Jump to:  
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum


Powered by phpBB © 2001, 2005 phpBB Group