dailysudoku.com

[George Woods]

Sorry folks can't see it Help

Get to this crunch point
078 050 010
500 041 000
106 072 035

850 406 100
064 517 980
701 008 564

007 185 206
085 060 701
610 704 358


Solve gives a hint 2 in r9c3, and I agree that a 9 here eventually creates a crash BUT I can't see any "logical" reason. I know this is probably a blind spot, but can't afford to waste more than an hour!

[Steve R]

George

I think I must have strayed in this puzzle because taking flight was the only way forward I could see.

In both the first and fifth rows there are just two cells for 2: column 1 or column 9. These rows between them ensure that the 2 in box 7 cannot occupy the first column.

I look forward to learning what I missed or whether perhaps the rules have changed to include X-wings.

Steve

[David Bryant]

There's an X-Wing on the "2"s, in row 1 and row 5 (cols 1 & 9). So there's either a "2" at r1c1 and a "2" at r5c9, or else there's a "2" at r1c9 and a "2" at r5c1. Either way there cannot be a "2" at r8c1, leaving r9c3 as the only possible spot for a "2" in the bottom left 3x3 box.

There's also a swordfish on the "9"s (in columns 1, 6, and 8 -- rows 1, 7, & 8) which allows you to set a "2" at r1c9, but the X-Wing is certainly easier to spot.

So far as I'm aware, this X-Wing (or swordfish) cannot be avoided -- at least, I can't find a simpler clue. I think that's a first for the Daily Sudoku! dcb

[keith]

I agree.

I get to a stage where there are two unique rectangles and an X-wing. I believe there is no "simpler" way to the solution.

Keith

[eddieg]

Help, I don't get the '2' in R9C3 as stated above by David Bryant. I still have the possiblity of R8C3 being a '2' as well as R9C3. Anybody see where I am going wrong?

078 050 010
500 041 000
106 072 005

850 000 100
064 517 980
700 008 564

000 180 206
080 060 001
610 000 358

[Steve R]

Eddie

You haven’t gone wrong but you do need to go a little further.

Have you identified the cells occupied by the pair (68) in row 2? Once this is done, it should be straightforward to develop the puzzle to the position posted by George at the beginning of this thread and so get to grips with the comments which followed.

Steve

[eddieg]

Thanks for the response Steve. I was overlooking exactly what you pointed out.

[Marty R.]

I might as well put my 2¢ in. After the initial elimination techniques, I noticed multiple X-Wing patterns, but they couldn't eliminate any candidates that I could see. There were also a couple of unique rectangles which I was unable to do anything with. I didn't look for swordfish yet, since it's such a hassle.

There was a "23" in r5c9 that looked promising as a starting cell for a forcing chain; the chain starting with the "2" left a "deadly pattern" and solving the cell with the "3" broke the puzzle wide open.

[jabejochke]

I was exactly at the point George outlined in the initial comments.

I hadn't yet moved to X-wings, Swordfish, etc. -- and I try not to. But the comments made by each contributor referenced the logic and not the name -- hence, I learned from those exchanges - and the solution makes sense.

This specific puzzle was referenced as 'very hard'. As it turned out, it was for me. But I had been sailing along on this one, while struggling with the May 1st puzzle. In reading the comments on the May 1st, the light suddenly dawned on me and I also understood the results to that one to.

Both puzzles were 'very hard' for me. And it really does not matter how they are classified. The important thing is that I can have the chance to ask for help when I hit the wall or offer help when needed.

I continue to learn a lot from the participants at this site.

Thanks,

Jack

[GREG N]

WHAT THE H*** IS AN X-WING OR SWORDFISH. I AM NEW AT THIS SUDOKU STUFF AND I SOLVED THIS PUZZLE BY TRIAL AND ERROR. THE WAY I BROKE IT OPEN WAS THERE COULD EITHER BE A 2 OR 9 IN R9C5 AND I GUESSED 9 WHICH BROKE THE PUZZLE OPEN FOR ME.
PLEASE LET ME KNOW HOW TO SOLVE THIS PUZZLE USING LOGIC ONLY.
THANKS,

[David Bryant]

Hi, Greg!

You really don't have to shout to get someone's attention.

Quite a bit has already been written about the "advanced techniques" -- you can read some of that stuff from the links provided in another message.

Here, I'll explain the X-Wing one more time. I'm assuming you arrived at the position George Woods posted at the beginning of this thread.

[keith]

After using all the techniques required in every previous Daily Sudoku, we get to here. Now what?

[TKiel]

Simple and multiple colouring on digit 2 solves it from where George Woods posted the grid. Don't know if that's easier or harder than X-wings and fish.

[Huw Llewellyn]

I try my hand at the Sudoku problems on this website and after a lot of practice, have managed to solve all bar the occasional Very Hard puzzle. The one on 2nd May was all but impossible!! I thought I was doing well to get to the point of needing a Swordfish! I can understand Greg N's frustration. Thanks to David Bryant for his help. I am perplexed by these "in" terms for special moves, and Swordfish and X wings are completely new to me. This has put back my proper work by hours and hours.

[keith]

There is a good introduction to solving techniques at the SadMan site:

http://www.sadmansoftware.com/sudoku/techniques.htm

Keith

[Marty R.]

[David Bryant]

[Marty R.]

[ravel]

Marty,

its a type 4 UR, because there are only the two 3's in column 4. So Davids chains can be written shorter:
r1c4=9 => r8c4=3 (=> r8c6=9 => r1c6=3 )
r8c4=9 => r1c4=3 (=> r1c6=9 => r8c6=3 )

Whenever you have a UR with a naked pair [39 above] in one row (column) and one of the numbers is strongly linked [the 3] in the other row (col), where there can be additional candidates, you can eliminate the second number from the UR corners in that row (col) [the 9].

[RogerC]

This is the hardest puzzle I have attempted - and the most fascinating discussion I have ever read!! Thanks to all the contributors; I have learned a lot.

There is one post I that I still haven't grasped yet from TKeil: