The New Sudoku Players' Forum

[bjschnei]

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

[Max Beran]

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

[Hud]

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

[bjschnei]

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

[Hud]

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.

[bjschnei]

the light goes on..thanks guys.

[bjschnei]

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

[bjschnei]

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?

[rubylips]

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

[MCC]

Hi bjschnei

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

xwing1 is in rows.
xwing2 is in columns.

[nj3h]

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?

[Ruud]

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.

[simes]

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

[bjschnei]

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

[Shazbot]

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.