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Christmas Killer 2017
http://www.rcbroughton.co.uk/sudoku/forum/viewtopic.php?f=3&t=1423		 Page 2 of 2
Author:  Andrew [ Fri Jun 01, 2018 6:47 pm ]
Post subject:  Re: Christmas Killer 2017
enxio27 wrote:
Going through Andrew's WT. I guess I'm not going to be able to solve this puzzle by myself.

I wrote:
2c. 17(5) cage at R1C2 = {12347/12356}, 1,2 locked for N2
enxio27 wrote:
Should that be N1, or am I misunderstanding something?
Apologies, my error, :oops: I was thinking of a different 17(5) cage when I typed that. It should be 17(5) cage at R2C5. I'll correct this, and any further errors if they appear, once you've finished going through my WT.

I wrote:
3a. R6C1 = {567} -> no 5,6,7 in R4C1 + R6C3
enxio27 wrote:
I have no clue how you are getting this. Please explain the logic.
In step 3 the 4 innies have three possible combinations, containing one of 5,6,7. R6C1 only contains {567} so the other three innies cannot contain any of these digits; R4C3 is already {12} so 5,6,7 are eliminated from R4C1 + R6C3.
I suppose, with hindsight, step 3a would have been clearer if I'd written it as 5,6,7 of {1237/1246/1345} must be in R6C1 -> no 5,6,7 in R4C1 + R6C3. I'll do that when I correct any errors.

Hope this helps. I'll keep my files open until you've finished going through my WT.


Also note that step 5 would have been simpler if I'd spotted R17C5 = {89} (hidden pair in C5). Then step 5 would because R7C5 + R8C6 = {89} (hidden pair in N8). I'll add a note about that to my WT when I update it.

Andrew
Author:  enxio27 [ Mon Aug 13, 2018 5:38 pm ]
Post subject:  Re: Christmas Killer 2017
Andrew wrote:
In step 3 the 4 innies have three possible combinations, containing one of 5,6,7. R6C1 only contains {567} so the other three innies cannot contain any of these digits; R4C3 is already {12} so 5,6,7 are eliminated from R4C1 + R6C3. I suppose, with hindsight, step 3a would have been clearer if I'd written it as 5,6,7 of {1237/1246/1345} must be in R6C1 -> no 5,6,7 in R4C1 + R6C3.

I guess I need to read up some more on innies and outies. I think that's where I'm hung up on this step.
Author:  Ed [ Tue Aug 14, 2018 7:50 am ]
Post subject:  Re: Christmas Killer 2017
Andrew wrote:
5,6,7 of {1237/1246/1345} must be in R6C1 -> no 5,6,7 in R4C1 + R6C3.
enxio27 wrote:
I guess I need to read up some more on innies and outies.
No need enxio! That won't help. It is only about those 4 cells. I still have to be very careful with these. Andrew is very good at this and does it methodically. I call it 'cage clean-up'. I usually only do it if I'm stuck.

Attachment:
XmasK2017.JPG
XmasK2017.JPG [ 26.86 KiB | Viewed 5981 times ]
The pic above is for that puzzle at the spot Andrew is talking about. I find it helpful to look at the numbers that can't be in a particular cell. If you take the two 5's in the black circles, they can only be in the combination {1345} since its the only combo with 5. But what will be left to go in r6c1? {1345} doesn't have a 6 or 7 to go in r6c1 if 5 is in r4c1 or r6c3. Therefore, both those black circle 5's can be eliminated. The same with the 6 & 7s in those cells. Each of them must go in r6c1 if their combination ends up being the correct one.

Good on you for sticking with this. Ask another way if it doesn't click.

Cheers
Ed
Author:  enxio27 [ Sat Dec 29, 2018 5:01 am ]
Post subject:  Re: Christmas Killer 2017
Ed wrote:
I find it helpful to look at the numbers that can't be in a particular cell. If you take the two 5's in the black circles, they can only be in the combination {1345} since its the only combo with 5. But what will be left to go in r6c1? {1345} doesn't have a 6 or 7 to go in r6c1 if 5 is in r4c1 or r6c3. Therefore, both those black circle 5's can be eliminated. The same with the 6 & 7s in those cells. Each of them must go in r6c1 if their combination ends up being the correct one.

NOW I finally see it! I've been beating my head on this wall off and on for months now. :brickwall:

I guess these combinations are what make killers so difficult. None of them are straightforward--you have to try each one, which to me seems closer to guessing than to logic. :?

I still have more to go, but at least now I'm one step closer. . .
Author:  Ed [ Sat Dec 29, 2018 6:00 am ]
Post subject:  Re: Christmas Killer 2017
Glad its clicked for you!
enxio27 wrote:
I guess these combinations are what make killers so difficult. None of them are straightforward--you have to try each one, which to me seems closer to guessing than to logic. :?.
I don't do much of this type of permutation analysis that has been the subject of these last few posts. It is not often required in order to solve an easier puzzle (ie, see my optimised walk-throughs that don't have this type of permutation analysis very often). I only do it if I'm getting desperate. Andrew does it routinely so he is very good at it.

Combinations (rather than permutations) are far more helpful but could also seem like guessing. I tend to only look closely to cages that I can get down to 4 combinations but that might be too many for your taste.

You are very persistent! An essential quality for solving harder killers....

Happy New Year!
Cheers
Ed
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