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 Difficult Killer Sudoku 28/8 
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Posted on: Sat Aug 29, 2020 3:40 am




Posts: 149
Joined: Sun Jan 31, 2016 7:52 am
Post Difficult Killer Sudoku 28/8
Over the last few weeks I have mentioned that the Friday Killer Sudokus have been easier than usual.

The 28/8 puzzle was rated 5 stars (196.3), but I thought it was very easy.

When looking at the steps required to complete the puzzle there was one step that required the adding of cages over several columns, but still quite straight forward, and one step with paired cell values within a 3x3 box. All the other steps are easy, and the 2 steps I mentioned are reasonably easy for a Killer Sudoku.


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Posted on: Sat Aug 29, 2020 5:11 am




Posts: 931
Location: Ladysmith, BC, Canada
Joined: Fri May 13, 2011 1:37 am
Post Re: Difficult Killer Sudoku 28/8
OMG.....another easy one!!!......not really all that keen on trying this one:)


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Posted on: Sun Aug 30, 2020 12:12 am




Posts: 691
Joined: Wed Apr 16, 2014 9:20 pm
Post Re: Difficult Killer Sudoku 28/8
When I can do the KS completely analytically then I am pleased with myself.
I ws able to do that on Friday's difficult puzzle.

That was not true of Sat's KS. I reduced to to three possibilities and had to do T & E on each possibility.

However, I do not really want harder puzzles on Friday. There are times when time runs short, and that just heightens my anxiety level. I don't think well when anxious. [wub]


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Posted on: Mon Aug 31, 2020 10:14 am




Posts: 149
Joined: Sun Jan 31, 2016 7:52 am
Post Re: Difficult Killer Sudoku 28/8
Quote:
That was not true of Sat's KS. I reduced to to three possibilities and had to do T & E on each possibility.


I agree that Saturday's puzzle was more difficult. Many of the steps required to solve that puzzle are more difficult than the hardest step for the Friday puzzle.

Below are some images to show the difference, the first image is what I considered the only step that was a little more difficult, 4&5 are paired values in cell f4 and in cage f5(6), so we can remove 4&5 from the other cells in the central 3x3 box (and also from column f if required later). From this point it is very easy to complete.

The next 3 images are 3 consecutive steps from the Saturday Killer, each of these steps uses more advanced techniques than anything in the Friday puzzle, and there is still some more work to go before it is solved. These are not the only difficult steps, I just chose these as an example because they are consecutive steps that result in many cells being solved.

Friday 28/8 (Difficult)
Image

Saturday 29/8 (Difficult)
Image

In the blue shaded cells there is a cross-pair with value 4, it is not your usual cross-pair because it is spread over 4 columns so it is easy to miss. The value 4 must be in either cage a4 or c4, and in cage f4, so we can remove it from g4 & g5.

Saturday 29/8 (Difficult)
Image

Another cross-pair (value 9)

Saturday 29/8 (Difficult)
Image
This is similar to before, there is a cross-pair with value 2, 2 must be in cage a4 or c4 and must be in cells g4 or g5.

These 3 steps solve several cells and gets it to a point that is close to complete.

I know "cross-pair" is probably the wrong term to use, somebody in the forum had suggested a better term but I have forgotten what that was.


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Posted on: Wed Sep 02, 2020 1:38 am




Posts: 691
Joined: Wed Apr 16, 2014 9:20 pm
Post Re: Difficult Killer Sudoku 28/8
michaele,
you caught something I did not with he cross wise 4s.
I was using B4 and D4 as my possibilities for T & E.
I try to catch those cross wise numbers as it really does help with solving the difficult KS. Not sure Why I didn't. maybe just being tiered and not quite up to snuff.


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Posted on: Wed Sep 02, 2020 5:10 am




Posts: 149
Joined: Sun Jan 31, 2016 7:52 am
Post Re: Difficult Killer Sudoku 28/8
Quote:
you caught something I did not with he cross wise 4s.


I had another look and it turns out both of us missed something, there was no need for a complicated cross pair with the 4. If you look at row 6 cell g6 can be solved, there is only one cell in the row that can be 4 (g6), b5/b6=3&6, and d6,e6 & f6 can not be 4 because of cage e4(4.8.9). After solving g6 the cross pairs with 2 & 9 will solve b4 and d4.


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