Having done sandwich variants before, I wondered if sandwich rules could be applied to an irregular sudoku.

The only way I found to do this do this was to have regions all one cell wide paths and it proved quite tricky to create an irregular sudoku with 9 regions with both that characteristic, and that didn't end in ambiguity for the crust locations, and I'm quite happy with the below result.

As it needed more information to solve completely, and I didn't want to just add normal row/column sandwich clues, I created "outer" sandwich clues using different digits for those sandwich crusts, and, between both sandwiches, the grid can be completed.

The digits for the outer sandwich can only be deduced once the inner crusts have been completed, so you could call this an "onion" sandwich :)

Hope you enjoy.

- Standard Irregular Sudoku rules apply - each row, column and specified regions must contain all the digits from 1 to 9 once only.
- Digits on the thermometers must increase from the bulb end to the flat end.
- Inner Sandwich
- Each region should be treated as a one cell wide path/line
- Numbers
**inside**the grid (in black) at the ends of each region refer to the sum of the digits sandwiched between the digits**1 and 9**for that region. (The sums are given at both ends simply for readability/ease of reference)

- Outer Sandwich
- Numbers
**outside**the grid (in green) refer to the sum of the digits sandwiched between the digits**X and Y**for that row/column (The colour has no relevance, and is just meant as a a visual reminder that the outer sandwich clues are for a different sandwich) - X and Y are not given, and need to be discovered:
- X is the row number that the digit 1 appears in the first column
- Y is the row number that the digit 9 appears in the ninth column

- In the example below, if the digits were found as follows, X would be 4, and Y would be 1, and therefore the outer clues would refer to the sum of the digits sandwiched between "1" and "4"

- Numbers

link to solve this online is available via Penpa at https://tinyurl.com/y9vt76zs

Lösungscode: row 1 (left to right) followed by row 9 (left to right)

Zuletzt geändert am 8. August 2020, 16:24 Uhr

Gelöst von Julianl, dm_litv, marcmees, Aporion, zorant, moss, NikolaZ, wenchang, kishy72, rimodech, bob, thayton8198

Zuletzt geändert am 24. September 2020, 21:00 Uhr

**am 24. September 2020, 17:42 Uhr von Big Tiger**

Well, I came over to try this one as a return favor ... but I am absolutely stuck. Right now I'd have to rate this as 5-stars because I have no idea how to get past the dozen digits I have on the grid so far.

@Big Tiger

Thanks for giving this one a go!

If you can let me know where you are (e.g. clone link from penpa) - in a hidden comment - I can edit that to give you specific pointers.

If you've got a dozen digits that would suggest you're at the inner sandwich, so as a general comment I'd ensure that you're shading/marking cells that can't be crust ends, as just like crusts in rows/columns can effect each other in a regular sudoku, regions can effect each other, just in different ways.

If you add a idden comment with current state I'll get back to you as soon as I can.