🥪 How to play Sandwich Sudoku

By Miguel Arechaga

Sandwich Sudoku is one of the most popular and clever sum-based variants of recent years. Its name comes from a very visual idea: the 1 and the 9 are the two slices of bread, and the numbers between them are the sandwich's filling. The clues outside the board tell you how much that filling adds up to. Here are the rules and a few tips.

What is Sandwich Sudoku?

It's a standard 9x9 sudoku where, next to some rows and columns, a number appears. That number is the sum of the digits between the 1 and the 9 in that row or column, not counting the 1 or the 9 themselves. The 1 and 9 are the "slices"; everything in between is the "filling."

Rules and how to play step by step

1. The sudoku rules apply: 1 to 9 without repeats in each row, column and 3x3 box.
2. The outer number on a line is the sum of the digits located between the 1 and the 9 on that line.
3. A 0 means the 1 and 9 are right next to each other (nothing in between).
4. You start with some clue cells and fill in the rest with logic. Every puzzle has a unique solution.

Tips to solve Sandwich Sudoku

• Everything revolves around the 1 and the 9: pinning down where those two "slices" go on each line is the heart of the puzzle.
• Sum of 0: the 1 and 9 are neighbors. Sum of 35 (maximum): they're at the two ends of the line, with everything else in between.
• The distance between the 1 and the 9 (how many cells lie between them) is also constrained by the sum: few cells can't add up to much, and many cells can't add up to little.
• Combine the sandwich sums with the classic elimination techniques of sudoku.

How it differs from regular sudoku

Compared to classic sudoku, Sandwich adds a layer of arithmetic tied to the position of the 1 and the 9, quite different from the cages of Killer Sudoku. If you enjoy sum-based variants, you'll also enjoy Little Killer Sudoku and Arrow Sudoku.