dailysudoku.com

[Micko]

Hello. I'm a bit new to this and sometimes I don't notice so much difference between the diffrent levels. But I recently tried "hard puzzle from Thu 8 Dec" and I took me very long time to solve. Much longer than any other I tried so far from any category. Anyone experinced the same?

I this sometimes yust the fact and how are puzzel levels set? Maybe it took me long time because I missed something as a beginer?

Regards, Micko

[David Bryant]

Hi, Micko!

Yes, I thought the December 8 puzzle was harder than the average "hard" puzzle on this site. If you indicate where you got stuck, I might be able to suggest a trick or two. :)

Samgj grades his puzzles with a computer program. You can gain more insight into the way that program works by reading this post and also this one over here. dcb

[amy]

Hey, I am stuck with this one and it is bugging me to no end!

I don't know how to draw these so that it will make sense, but here goes...

I have:

5 - 2 - 4 1 - 8 7
8 - 3 - - 5 - - -
- 1 - 9 - - - 5 6
- 4 5 8 - - - - 9
- - - - 5 - - - -
2 - - - - 4 - 3 5
1 5 - 4 - 2 6 9 3
- - - - - - 5 2 4
- 2 - 5 6 - 1 7 8

[David Bryant]

Hi, Amy!

You can get your posts to make more sense by using the "code" and "/code" tags -- read the FAQ to learn more about those.

Here are two suggestions about how to proceed with this puzzle.

-- You can put a "1" at r6c4. Counting up the explicit possibilities, it appears that r6c4 could contain the values {1, 6, 7} -- all the other values already appear in row 6 or in column 4 somewhere. But you can eliminate the possibility of a "6" because the "6" in column 4 must appear in r1c4 or r2c4 -- there's no other way to fit a "6" in the top center 3x3 box. And you can eliminate the "7" because of a pair {7, 8} appearing in r6c2 & r6c7. That leaves "1" as the sole candidate for r6c4.

(Have you spotted the {7, 8} pair in row 6? It's easy to spot at r6c7. The logic at r6c2 is a little more complicated -- it depends on the "hidden pair" {6, 9} lying in r1c2 & r2c2.)

-- Do you know about X-Wings? If so, you can find an X-Wing pattern in the "2"s at r3c5, r3c7, r4c5, & r4c7 -- those are the only places a "2" can fit in row 3, and also in row 4. So either there's a "2" at r3c5 and another "2" at r4c7, or else there's a "2" at r4c5, and another "2" at r3c7. Either way we can eliminate the other possible "2"s from columns 5 and 7 -- this reveals a "7" at r2c5 and also allows us to cross off a possible "2" at r2c7 and at r5c7.

That's probably enough to get you rolling again. dcb

[Philmac]

I had exactly the same position as Amy. You may remember me, the one who confused himself with too many digits a few weeks ago! Same thing happened again here. Normally, BEFORE I resort to filling in possibilities I spot things like 6 must go in r1c4 or r2c4 so that rules out 6's in for the remainder of that column .. but after having filled in all the possibilities the 6's stubbornly refused to go away in r5c4 and r6c4!! A lesson learned(again!).

I have never been able to use xwing (well not explicitly anyway, I usually find that it tells me nothing that I don't already have coded up), but the example you give is one place where I could have used it and missed it!
Must get my mind organised!

Thanks again for your wonderfully clear help.

It's gone pretty mild here in England and everyone's started talking about avian flu again.

Phil

[David Bryant]