Easy Peasy Sudoku Advent (13) - Zipper Lines ++
(Published on 13. December 2025, 06:00 by Richard)
This sudoku advent calendar contains 24 variants that were included in my Sudoku Variants Series (SVS) but turned out to be too hard to be solved by a wide range of puzzlers. I aim for difficulties of 1-2 stars and have written some general and/or specific hints as well. I hope some players will try the original SVS puzzle #449 after solving the advent version.
Zipper Lines ++
Specific hint for this puzzle:
The line starting in box 7 covers all cells of that block. So a consecutive chain of 5 numbers adds to 45 and you can easily calculate the starting digit in R8C1 plus the total sum of the digits on the same line in box 8. Hence: the 3 remaining digits in box 8 (R789C6) are known and can all be placed.
Apply classic sudoku rules.
The sums of each pair of digits coming out from the center (indicated by a diamond) of a Zipper plus line increases by one.
E.g.: if the single center cell contains an 8, the sums of the pairs go up to 9, 10, 11 etc. If the sum of the central pair of digits is 6, the sums of the next pairs go up to 7, 8, 9 etc.
Digits may be repeated on lines.
Solution code: Row 1
Comments
on 20. December 2025, 23:39 by SennyK
I think I have become a sucker for your puzzles. Thank you for all the lovely puzzles you publish! :-)
on 15. December 2025, 23:17 by Dee_Code
This one had one of the smoothest flows of the series so far once you get one digit in past the first 6 digits, it flowed so fast
on 15. December 2025, 19:32 by dzamie
A little intimidating at the start, but goes surprisingly quickly once you place a couple of digits. Useful to keep notes for at least the first long zipper.
on 14. December 2025, 00:21 by TheJRMY
Zipper is one of the two mechanics that my brain just does not process at all, so I’m not solving this one, but wanted to say that I love the name. I assume you write code?
on 13. December 2025, 23:55 by RockyRoer
if (puzzleAuthor == Richard) {puzzle.addToQueue();
SolveCount++;}
on 13. December 2025, 22:29 by TheJRMY
Zipper is one of the two mechanics that my brain just does not process at all, so I’m not solving this one, but wanted to say that I love the name. I assume you write code?
on 13. December 2025, 13:27 by wuc
Great constraint. To me steady 2* difficulty. Great setting thx.
on 13. December 2025, 12:59 by Franjo
The first steps on the path indeed were easy-peasy, but the rest? Way more than 1* for me! But also a great pleasure to solve. Thank you very much for creating and sharing this lovely puzzle.
And now I realize that I already had solved the original one - and had given one star less than the average for that! Maybe today my brain works in slow motion?
on 13. December 2025, 06:54 by Richard
When SVS #449 was just published and players commented that they needed to guess, I solved it myself once more and found (in hindsight) that it contains a few too tricky (although beautiful!) steps. At that moment I was at two thirds of writing all the calendar puzzles and decided to add this type to the list 'to make it up with those who struggled their way to completion of SVS #449'. :-)
on 13. December 2025, 06:42 by Klausku
That‘s a very interesting constraint. I may try the original one. Thanks for this easy snack.
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Reply: Thanks for the quick solve. In hindsight, the original SVS contains a few steps that are too hard to spot, and because of that some players have guessed their way to the finish. Although it is perfectly logic solvable. Be warned. :)
on 13. December 2025, 06:22 by Nylimb
As someone who hasn't yet solved SVS #449, I appreciate this easy introduction to the constraint. I'll have to give the other one another try. Thanks!
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Reply: You are more than welcome to ask for a hint in case you got stuck!
