What Is Sandwich Sudoku?

Sandwich Sudoku is a Sudoku variant where you are presented with extra numbers outside of the grid aligning with the rows and columns. Such as in the example below. 

These red numbers outside the grid indicate the sum of the digits ‘sandwiched’ between the 1 and the 9 in the corresponding row or column. This is why this variant is also sometimes known as ‘Between 1 and 9 Sudoku’. 

So, for example, if you look at the rightmost column, you’ll see that the sandwich clue for that column is 12. And in this particular column, the digits 1 and 9 as well as all the digits between them are given. So you can see why the sandwich clue is 12 as the digits 8 and 4 sum (in other words, ‘add up’) to 12. 

It doesn’t matter which order the 1 and the 9 are in either. 

If you look at the third row from the top, the sandwich clue is 0 as the 1 and 9 are given (this time in a different order) and there are no digits between them. 

Typically, clues will not be given for every row and column, especially if the 1 and 9 are already given in the particular row.

Solving a sandwich sudoku

With a bit of basic maths, the additional hints on each puzzle can actually make it easy to solve the puzzles.

This is because they’re not adding additional constraints or difficulty to the puzzle but are instead providing additional information you can use to solve the puzzle. 

For example, if you see a 0 sandwich clue, you immediately know the 1 and the 9 must be directly next to each other in that row or column. Or if you see a 3 you know the 3 must appear between the 1 and the 9. 

Where to play

You can find plenty of Sandwich Sudoku puzzles to solve over at Krazydad.