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An entry in Fortnightly Topic Challenge #47: "Wacky Sudokus"

Other puzzles in this series



Welcome to the seventh puzzle in this series! For more information about the series, see the first puzzle and the introduction. Enjoy!

Halfway through now! The puzzles so far have been somewhat of an introduction to these wacky sudokus, time to start stepping it up a notch! The next puzzles are going to be harder, not all the same difficulty, but all just as wacky!


            enter image description here


Mmmmmm... nothing tastier than a bit of 2-8 between two slices of 1 and 9

Google Sheets Link


RULES

  • Normal Sudoku rules apply
  • The numbers on the outside of the grid show the sum of the digits 'sandwiched' between 1 and 9
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First, let's take a look at the rows and columns with 0s

They must have the 1 and 9 right next to each other. We can actually determine the exact placements of the 1 and 9 for each. In C5 and R6 one side of the existing 1 is blocked. In C1 and R9 one side of the existing 9 can't have a 1 because of sudoku rules. In C8 the 9 must now go in the bottom-right 3x3 box, and there is only one way to fit a 1 near it without contradicting row clues.
step 1

Now,

I got to here with plain "This is the only place for <number> to go in this box/row/column" logic.
step 2

Let's use the top-edge clues once again!

From left to right: The 1 in C3 must go on the top, so that all of 2-8 (summing to 35) can sandwich between 1 and 9. The only way to sandwich a 4 in C4 is to sandwich a single 4, and there is only room for that to happen in one way. The 9 in C7 must be the bottom of the sandwich as below it sums to more than 6. The sandwich must use the 2 above; the only way for a sum of 6 is 2+4 so that can be placed. In C9 there is already a sum of 13 below the 9, and a 1 will finish that sandwich.
step 3

After that,

Another round of plain "This is the only place for <number> to go in this box/row/column" logic.
step 4

Now to use the left-edge clues

From top to bottom: R1 has a sum of 11 to one side of the 1 which can be safely sandwiched away. The 9 in R3 must be on the left side of the 1 to allow for a large enough sandwich, and there is only one spot that it can be placed due to sudoku logic. Both the 1 and 9 in R7 are there, and the sum of 10 can be completed as 6+4.
step 5

To wrap it all up,

The rest of the sudoku can now be completed with "This is the only place for <number> to go in this box/row/column" logic.
complete solution

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