dailysudoku.com

[Louise56]

I'm trying to solve this one and have a question for one of you experts. These are my bottom three, 3x3 boxes

-/-/- 359/2/1 389/-/6
9/6/- 35/7/358 -/-/4
-/-/1 4/6/3589 389/7/238

My question is with the 9's. In row 7 I have a 9 in r7c4 and r7c7. In row 9 I have a 9 in r9c6 and r9c7. These are the only 9's in rows 6 and 9. It looks like an X-wing set up, but in the middle box the 9's are not in the same column. But since they are in the same 3x3 box, it seems like I could treat this like an x-wing, but I don't know if I can eliminate the remaining 9's in column 4 or column 6. Does this setup have a name? Thanks!

[someone_somewhere]

Hi Louise,

That was real a nice question!
I was working a lot on X-wing.
You made a nice discovery. The X-wing that has the same number at intersection of 2 rows and 2 columns (the name cames from the airplains flying in this formation) and having this same number ONLY 2 times in the rows or in the columns - permits us to eliminate the rest of this number from the 2 columns respective 2 rows (if there are any additional such ones).

I think that one of the "generalization" of this X-wing is the technique called "intersectioon of four groups". It is the combination of 4 intersection rows, columns, 3x3 blocks.

* If we have 2 rows and 2 columns - then we speak about the "X-wing".

The other cases are:

* 2 rows, 1 column & 1 block

* 1 row, 2 columns & 1 block

* 2 rows, 2 blocks

* 2 columns, 2 blocks

Let's take an example:

X-X
6=6======
X-X
=== the sign "=" means no "6"
==6
6==
X-X
X-X
X-X

We have here number 6:
- in row 2 exact twice
- in column 1 exact twice
- in column 3 exact twice
- in 3x3 block (4,1) - (6,3) exact twice
We have the same number 6 at the intersection of four groups:
one row, 2 columns and 1 3X3 block.

We can quickly deduce that from all places marked with "X" the "6" can be eliminated!

For the rest of the cases, I let you draw your own diagrams.

see u,

[zigzagpython]

still not understand!!!!
I spent nearly an hour on the sheet
only found 1 in r6c2, 9 in r1c9 and most easily 6 in r8c2
then move no step

help me Mater

[someone_somewhere]

Hi,

Please post me the initial position.

see u,

[someone_somewhere]

Hi,

Sorry, now I see which puzzle you have problem with.

080016700
600030005
100890000
320000500
006000200
008000097
000021006
900070004
001460070

6 in r8c2 - Unique Horizontal
4 not in r4c6, it is in r4c5 or r5c5 or r6c5 (Column on 3x3 Block interaction)
4 not in r5c6, it is in r4c5 or r5c5 or r6c5 (Column on 3x3 Block interaction)
4 not in r6c6, it is in r4c5 or r5c5 or r6c5 (Column on 3x3 Block interaction)
5 not in r5c4, it is in r5c5 or r6c5 (Column on 3x3 Block interaction)
5 not in r5c6, it is in r5c5 or r6c5 (Column on 3x3 Block interaction)
5 not in r6c4, it is in r5c5 or r6c5 (Column on 3x3 Block interaction)
5 not in r6c6, it is in r5c5 or r6c5 (Column on 3x3 Block interaction)
8 not in r4c6, it is in r4c5 or r5c5 (Column on 3x3 Block interaction)
8 not in r5c6, it is in r4c5 or r5c5 (Column on 3x3 Block interaction)
1 not in r4c8, it is in r4c9 or r5c9 (Column on 3x3 Block interaction)
1 not in r5c8, it is in r4c9 or r5c9 (Column on 3x3 Block interaction)
1 not in r6c7, it is in r4c9 or r5c9 (Column on 3x3 Block interaction)
2 not in r2c8, Hidden Pair 1 8 in r2c7 and r2c8 (in Row)
4 not in r2c7, Hidden Pair 1 8 in r2c7 and r2c8 (in Row)
4 not in r2c8, Hidden Pair 1 8 in r2c7 and r2c8 (in Row)
9 not in r2c7, Hidden Pair 1 8 in r2c7 and r2c8 (in Row)
4 not in r6c2, Nacked Pair 4 5 in r6c1 and r6c5 (same Row)
5 not in r6c2, Nacked Pair 4 5 in r6c1 and r6c5 (same Row)
4 not in r6c7, Nacked Pair 4 5 in r6c1 and r6c5 (same Row)
1 in r6c2 - Sole Candidate

and from here on, you can swim alone...

see u,

[zigzagpython]

thx for yr tips
'5' in either r4c5 or r5c5
'1' in eihter r4c9 or r5c9
they are important tips and main numbers blocking my going

need more training la
but next week will be very busy.
loads work and have a test from my part time studying in the coming weeks:cry:
got little bit injury from yesterday's rugby match.

see you master

[David Bryant]

[junior]

[David Bryant]

[Louise56]

Thanks Someone for an excellent explanation. This was my favorite puzzle to date! I'm always looking for patterns and shortcuts.

[scorpio56xxl]

Hi Louise,
I have the same problem as you but I come to another conclusion. Since
in r3c5 there is a nine so there could not be one in r4c5 - r6c5. So the nines in the middle box goes in r4c4/r5c4 and r4c6/r5c6. Box number 8 and 9 the last one contains possible nines as you described. So there couldn't be a nine in r9c9. Since there is a nine in box 7 which intersects r9, box 6 which intersects c9 and an intersection between the boxes 8 and 9 the nine for the last column must be placed in r1c9. But I could't see that you can eleminate the nines in the middle box. I 'm looking forward to getting your answer. Thanks in advance.

[Louise56]

Hi Scorpio,

I don't remember all the steps I took to solve the puzzle. I do remember finding a 7/9 pair in r4c6 and r5c6 and that helped me to elimate the 9 in r9c6. That put a 9 in r7c4 and a 9 in r9c7. I hope that helps!

[David Bryant]

[alanr555]

[Blackfoot]

[David Bryant]

There's no need to apologize -- all of us were new to this at some point.

Concentrate on row 6. With the {4, 5} pair placed in r6c1 and r6c5, there are only four numbers left -- {1, 2, 3, 6} -- to fill in the four open positions in the row (that is, the values {1, 2, 3, 6} must occupy the cells r6c2, r6c4, r6c6, & r6c7 in some order).

Now look at r6c2. It has to be a "1", a "2", a "3", or a "6." It clearly can't be either a "2" or a "6" because those values already appear in column 2. And it can't be a "3", either, because there's already a "3" in the middle left 3x3 box. So it has to be a "1." dcb

PS I have some trouble with this idea still -- it's easy to eliminate possibilities by looking up and down columns, or left and right across rows. It's a bit harder to remember to look all around the 3x3 box for additional numbers that can safely be eliminated from a list of possibilities. One set of eye motions comes naturally -- I have to work at the other one. Maybe crossed eyes would help!

[someone_somewhere]

Hi,

just take a look again at the steps that I
Posted: Sun Oct 16, 2005 9:18 am

that should answer your question about placing the "1".

see u,