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Difficult Killer Sudoku 31/7
https://www.calcudoku.org/forum/viewtopic.php?f=16&t=1257		 Page 2 of 2
Author:  michaele  [ Sun Aug 02, 2020 12:07 pm ]
Post subject:  Re: Difficult Killer Sudoku 31/7
Quote:
I realised that the 22 cage starting at b2 had to be 123457


With large cages I find it is worth thinking about what is not there as much as what is. For example in the b2 cage it has six cells so there are 3 values not in the cage that must add to 23, and the only 3 unique values for 23 are 6,8 & 9, that makes it easy to know that the values in the cage must be 12345&7. Another example would be the f8 cage (38), it has 6 values so it is missing 3 values that add up to 7, so the cage is missing 1,2 & 4.

Large cages can look difficult and they seem to increase the difficulty rating a lot, but they can be very helpful. When starting a Killer Sudoku puzzle the first thing I do is look for small cages with only 1 or 2 possible combinations and large cages that can be helpful.
Author:  eclipsegirl  [ Sun Aug 02, 2020 3:26 pm ]
Post subject:  Re: Difficult Killer Sudoku 31/7
Paul,
That 22 cage was critical. Michaela is correct, I look at those cages and try to figure out if there is a unique combo for the entries.
Author:  paulv66  [ Sun Aug 02, 2020 9:49 pm ]
Post subject:  Re: Difficult Killer Sudoku 31/7
eclipsegirl wrote:
Paul,
That 22 cage was critical. Michaela is correct, I look at those cages and try to figure out if there is a unique combo for the entries.


Absolutely. That's how I managed to crack the puzzle. I think I was a bit thrown by Michaele's comment about how straightforward and expected it to fall into place straight away. But you're both right that the large cages are often the key and that the simplest way to approach these is to work out what numbers are NOT in the cage.
Author:  michaele  [ Mon Aug 03, 2020 12:12 am ]
Post subject:  Re: Difficult Killer Sudoku 31/7
Quote:
That 22 cage was critical


I had another look, and from the position of my last image (after placing 2&6 in the i5 cage) it can all be done very easily. The b2(22) cage can be ignored, all of those cells can be solved without considering the total for the cage.

Later today I will post a list of steps to complete the puzzle.
Author:  michaele  [ Mon Aug 03, 2020 9:44 am ]
Post subject:  Re: Difficult Killer Sudoku 31/7
I had said I would list all the steps, but there are too many to list without being too boring. So here are few images at various stages during the solving process to give people an idea of what I did. Apart from at the beginning when I calculate the pencil marks for cage f8(38), the 3 large cages play no further part in solving the puzzle, all cells in b2(22), d7(32) & f2(38) are solved when they are the only cell remaining within a row or column that can be that value. For example in the second image b2 can be solved because no other cell in row 2 has the value 3.

So here are some progress images, if anybody is interested in knowing more I am happy to give more information.

Image

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