CageDokuSandwich Sudoku Rules and Tips
By Andrew Boyko, developer of CageDoku · Updated
In Sandwich Sudoku the clues sit outside the grid. Each clue gives the sum of the digits sandwiched between the 1 and the 9 in that row or column.
The rules
- Every row, column and 3×3 box contains 1 to 9 once.
- A clue next to a row or column is the sum of the digits that lie strictly between the 1 and the 9 in that line, in either order.
Technique 1: clue 0
A clue of 0 means there is nothing between the 1 and the 9: they are neighbours.
Technique 2: the largest clue
The digits between the 1 and the 9 are chosen from 2 to 8, so the largest possible clue is 2 + 3 + … + 8 = 35. A clue of 35 means the 1 and the 9 sit at the two ends of the line. A clue of 1 can never occur, since the smallest digit between them is 2.
Technique 3: small clues
A clue of 2, 3 or 4 is a single cell holding that digit, because the digits between the bread run from 2 to 8 and cannot repeat. A clue of 5 is either a single 5 or the pair 2 and 3, and so on. Combine this with the number of cells between the bread.
Technique 4: bread positions
If a 1 is placed, the 9 can only be at certain distances so that the cells between add up to the clue. Work out which positions of the 1 and 9 are consistent with the clue and cross out the others.
Practice
Hints in CageDoku explain each sandwich step and show the cells in between. Try a Sandwich puzzle in your browser.
Frequently asked questions
Which digits are in the sandwich?
Digits 2 to 8, since 1 and 9 are the bread.
What is the maximum clue?
35, when the 1 and the 9 are at the ends of the line.
Practice it in CageDoku
Free, ad-free Killer Sudoku and seven more variants. Hints name the technique and highlight the cells, so you learn why a digit goes where it goes.