Sandwich Sudoku

Sandwich Sudoku. Clue numbers outside a row or column give the sum of digits "sandwiched" between the 1 and the 9.

How to play

Fill the 9×9 grid so every row, every column, and every 3×3 box contains the digits 1 to 9 with no repeats — the classic Sudoku rule. Sandwich Sudoku adds one twist: Clue numbers outside a row or column give the sum of digits "sandwiched" between the 1 and the 9.

Sandwich sudoku wraps an ordinary 9x9 grid in clue numbers printed outside the rows and columns. Each clue is the sum of the digits trapped between the 1 and the 9 in that line — the 1 and 9 act as the two slices of bread, and everything caught between them is the filling. The twist is that a clue never tells you where the bread is, so most of the work in sandwich sudoku is figuring out where the 1 and 9 sit before the sum even makes sense.

How to solve Sandwich Sudoku

Read every clue as a distance as well as a sum: a 0 means the 1 and 9 are adjacent with nothing between them, while a 35 forces them to the two far ends so that all of 2-8 (which total exactly 35) fit inside. Because the filling can only use the digits 2-8, some clues are impossible — a 1 or a 34 can never appear — and small clues like 2, 3 or 4 must be a single sandwiched digit, which pins the 1 and 9 exactly two cells apart. For a general clue, list every run of consecutive cells whose sandwiched digits can reach that total; this fixes how far apart the crusts stand even before you know which end holds the 1 and which holds the 9. It often pays to work the complement instead: the digits outside the sandwich sum to 35 minus the clue, so a large clue strands only a couple of digits out on the ends. Cross these length constraints with ordinary row, column and box logic to lock the 1 and 9 into place, and the filling digits then fall out.

Every Sandwich Sudoku puzzle is free to play in your browser — no ads, no sign-up, and it works offline.

Frequently asked questions

What is Sandwich Sudoku?

Sandwich sudoku is a 9x9 variant in which a number beside a row or column gives the sum of all the digits sitting between the 1 and the 9 in that line. You still fill every row, column and box with the digits 1-9, but you also use those outside sums to locate the 1 and the 9 — the 'bread' — and the filling squeezed between them. Nailing down where the crusts sit is what turns each clue from an abstract total into a concrete placement.

What does a clue of 0 mean in Sandwich Sudoku?

A 0 clue means there are no digits between the 1 and the 9, so they occupy adjacent cells, in either order. It is one of the strongest clues on the board because it collapses the two crusts into a single neighbouring pair; combine it with box logic and you can often fix both the 1 and the 9 straight away.

Which sandwich clues are impossible?

Since the filling can only contain the digits 2-8, a clue of 1 can never occur — no available digit sums to 1 — and neither can 34, because reaching it would mean taking the full 2-8 total of 35 and removing a digit worth 1, which does not exist. Valid sandwich clues are 0 and then 2, 3, 5 and upward to 35. Knowing that 1 and 34 are off the table lets you rule out placements a naive count might otherwise suggest.