Easy Peasy Sudoku Advent (20) - Assorted Sandwiches
(Published on 20. 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 #303 after solving the advent version.
Assorted Sandwiches
General hint for this type:
Like with other sandwiches, it is important to count the sandwiched digits and the crust digits together to calculate the sum of the digit(s) that have to be placed at the border(s), and how many digits form that remaining sum, given the fact that the crust digits cannot be part of the remaining sum.
The sandwich of 36 in R1 is of course the best place to start, combined with the clue of 35 in C1. After that the two bottom rows are the best places to proceed, combined with C9.
Apply classic sudoku rules.
Clues outside the grid indicate the presence of a sandwich in the corresponding row or column. A sandwich has two digits that act as its boundaries. The clue is the sum of all the digits between those boundaries. The boundaries are the two individual digits of the clue, in any order; 31 outside the grid means that the sum of the digits placed between the digit 1 and the digit 3 (order is not given) is 31.
A sandwich of 28 for example has a total sum of 28+2+8=38, leaving 7 out. That can be {1,6} or {3,4} or {7}.
Sudokupad (no answer check)
Sudokupad (with answer check)
or
Penpa+.
Solution code: Row 4
Comments
on 21. December 2025, 13:00 by Tobias
Great solution path, beautiful!
on 21. December 2025, 07:27 by Richard
Thanks for all the comments on the solution code discussion. The suggestions and points of view provide more 'food for thought' for me. :)
on 20. December 2025, 21:23 by CitrusGremlin
thank you for finishing off with some with solution check on. I do solve the ones I can without it, but having it on is such a handy learning tool.
on 20. December 2025, 21:14 by SennyK
Hello Richard! I really enjoy your puzzles, I think they are all very interesting and well constructed! As to the solution checking topic - I would like to encourage you to use two different names for puzzles with and without solution checking - this might be the little (sc) on the end of the version with solution check. This would allow you to see how many solves each of the versions get, as puzzles with different names get different solve counters. Just a thought :-)
on 20. December 2025, 16:47 by mihel111
Lovely puzzle, Richard. And what an interesting topic in the comments about answer check. At first, I was thinking "Why is Richard so lazy he is not providing answer check ?". Now I see the point. And obviously, the debate that emerges. I can see good arguments in both sides. May I also say that the answer check is not the only help man can get. Sven's software also provides the possibility of red-ifying (a Simon word) pencilmarks. All those helps may be considered as cheating, but may also be considered as beginner friendly (the notion of beginner being variable according to the difficulty of the puzzle you are facing). Maybe the solution to resolve this issue is technical. Could it be possible to differentiate final answer check (with a grid full of big digits) and partial answer check ? Could it be possible to allow or not the partial answer check in Sven's software ? Could it be possible for the author of a puzzle to allow or not those helps ? Is it possible that Sven's software granted you with a gold star if you conquer a puzzle without any help, a silver star if you use partial answer check and a bronze star if you use the pencilmark conflict checker ? After all, a solve without any help should be rewarded in some way.
In the actual state of the world, I think the choice of providing an answer check belong to the author. People may like or dislike the choice made. So it is. For the rest, may Holy Sven come to our rescue.
on 20. December 2025, 16:26 by abihummel
Probably my favorite of this series so far. So smooth!
on 20. December 2025, 15:29 by Br1312te
Generally, I use solution checking for two reasons:
1) to check if I understood the rules correctly. This usually occurs at the start of a puzzle and after I feel confident about MY internal logic process. I'm just checking the foundations. I don't consider this cheating.
2) to find mistakes. Straight-up, I do consider this cheating. However, 90% of my mistakes are typos or basic scanning mistakes. My enjoyment in variant sudokus drives from the logic intricacies; the more basic sudoku steps I care less about. The reality is that when I have to start over because of a typo, I just don't.
For your puzzle series I did relish the opportunity to practise finding mistakes when they occurred (which I do consider a skill). I think I felt comfortable here to do so because there was the reasonable guarantee of a very high quality puzzle. I do not wish for this to become the standard for all creators, though.
For the puzzles that I design, I do include solution checking. I do enjoy seeing people discover my solve path and enjoying my logic flow (and I hated seeing Mark brute force my puzzles on two occasions), but for the most part, I've had my fun while designing the puzzle. I can make something I enjoy, and enjoy the process of making it, but then it's up to the solver to find their own enjoyment. If that involves guessing, finding mistakes, or checking every step they make, that's up to them.
on 20. December 2025, 14:00 by Rollo
Ganz toll konstruiert, das flutscht! (Das schönste an der deutschen Sprache ist die Onomatopoesie ... ;-), sagte glum_hippo einmal)
on 20. December 2025, 11:21 by Klausku
Very nice. After the first steps I was confused until I realized that my normal sandwich solving technique didn’t work.
on 19. December 2025, 18:57 by Richard
After the comments in the last few days about the use of answer checking, I have provided a link to Sudokupad with an answer check as well. Since not everybody wants to have the chance to use it, there is also the link without it. I still have some reservations about the use of it, since it is now possible for each and everyone to 'solve' a puzzle in a few minutes while guessing. But for the last five episodes of the advent calender, I will use this as an experiment.
