Sudoku with extra rule

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Sudoku with extra rule

Postby urhegyi » Wed Jan 06, 2021 2:17 pm

Here a post from the sudoku puzzles forum. I have solved it with 2 assumptions I had to prove with trial and error. I look forward to see a way of solution only by logic. I will publish my hidden solution. Can anyone check if I have made no errors?
santa.jpg
santa.jpg (85.04 KiB) Viewed 89 times

Description:
Normal rules apply, plus orthogonal neighbours to even digits must be odd. I’ve given you a head start with notation and color-coding even-odds. You’ll make good headway if you remember that each house must have 4 even and 5 odd, and given the additional rule it forces certain patterns.
Solution:
Hidden Text: Show
Code: Select all
132547698
547698123
698123574
321456789
874931256
965872341
419765832
783214965
256389417
urhegyi
 
Posts: 220
Joined: 13 April 2020

Re: Sudoku with extra rule

Postby creint » Wed Jan 06, 2021 10:48 pm

Initial clear of pencilmarks for extra rule:
Code: Select all
123456789 13579     123456789 13579     2468      13579     6         9         8
13579     123456789 13579     2468      9         2468      1         123456789 13579
123456789 13579     123456789 13579     2468      13579     123456789 13579     123456789
13579     2468      13579     123456789 13579     6         13579     8         9
2468      13579     4         13579     123456789 13579     2468      5         2468
13579     2468      13579     123456789 7         123456789 13579     2468      13579
123456789 13579     123456789 7         2468      13579     123456789 13579     123456789
7         123456789 13579     2468      13579     2468      9         123456789 13579
123456789 13579     123456789 3         2468      13579     123456789 13579     123456789

Digits 2468 are revealed, so all cells with 2468 are known in box 2468.
Digits 13579 is inverse so can be excluded too. 5 cells and sometimes 4 of the 5 cells.
After that singles and sets and solved.
creint
 
Posts: 230
Joined: 20 January 2018


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