Sudoku Players' Forum (clone)

by **bjschnei** » Wed Dec 07, 2005 10:05 pm

Been working on this one for a while...can't figure it out
can anyone help?

by **Max Beran** » Wed Dec 07, 2005 10:46 pm

Presumably because you didn't notice the x-wing. Find it and the puzzle falls to pieces.

by **Hud** » Wed Dec 07, 2005 10:49 pm

Is there a nice x-wing of 4 in row 1 and 9?

by **bjschnei** » Wed Dec 07, 2005 11:03 pm

Well..i am looking at the number 4..and granted..i have never actually solved an x-wing before which i part of my problem here....

but how do i know the x wing is in rows 1 and 9 and not rows 2 and 8

by **Hud** » Thu Dec 08, 2005 12:11 am

Can't be in rows 2 and 8 since there are more than 2 4's in each row. For an x-wing, there must be 2 of the 4's in each row and they also must be in the same column. You can then eliminate all 4's in those 2 columns except the x-wingy ones.

by **bjschnei** » Thu Dec 08, 2005 12:19 am

the light goes on..thanks guys.

by **bjschnei** » Thu Dec 08, 2005 12:22 am

umm..light went off...
there are only 2 4's in column 1, and 9 though...

by **bjschnei** » Thu Dec 08, 2005 12:25 am

i was thinking that it is kinda a double xwing?

xwing1 r1c3 r1c8 r9c3 r9c8
xwing2 r2c1 r2c9 r8c1 r8c9

r2c8 and r8c3 are left out..so 4 can be eliminated from both...is that the correct logic to be using here?

by **rubylips** » Thu Dec 08, 2005 12:41 am

xwing1 allows 4 to be eliminated from r2c8, r2c3 and r8c3, after which the puzzle is trivial to solve.

by **MCC** » Thu Dec 08, 2005 1:17 pm

Hi bjschnei

Both xwing1 and xwing2 are valid and eliminate the same candidates.

xwing1 is in rows.
xwing2 is in columns.

by **nj3h** » Thu Dec 08, 2005 3:53 pm

Unless I typed it wrong (and I've checked 3 times) the puzzle is rated diabolical using Sadman's Sudoku. His solver says it takes trial and error to solve it.

5..13...9
.3...8...
....94.3.
.439...6.
..876349.
.6.4..32.
.7.84.91.
.9.2...5.
6..3.9..2

Strange. I wonder what is going on here?

by **Ruud** » Thu Dec 08, 2005 8:07 pm

Check a 4th time, just to be sure.

This is what the Sudo Cue analyzer tells me:

3 Line-Box interactions.
1 X-Wing.

The rest is hidden/naked singles only.

Ruud.

by **simes** » Fri Dec 09, 2005 7:17 pm

nj3h wrote:Unless I typed it wrong (and I've checked 3 times) the puzzle is rated diabolical using Sadman's Sudoku. His solver says it takes trial and error to solve it.

I've found a typo in the optimisation in the XWing routine, it wasn't even checking for one.

Thanks for pointing it out!

S

by **bjschnei** » Sun Dec 11, 2005 2:31 am

using sadman's sudoku...can't make sense of what the software is suggesting as the next move...can any one else explain it?

by **Shazbot** » Sun Dec 11, 2005 3:07 am

The XY Wing technique will allow you to eliminate 6 as a candidate from r4c6, leaving a naked single (9) in that cell. This then eliminates 9 from r3c9, leaving a 1.

Why Sadman offered the 1 instead of the 9 I don't know, since the 1 was only apparent AFTER the 9 had been placed.

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