The Doppit Almanac · No. 34

Crustit, a free daily sandwich sudoku

Count what sits between the crusts

What it is

Crustit is sandwich sudoku. The grid fills like any sudoku, each row, column and box holding every number once, but around the edge sits a number for every line. That clue is the sum of the digits caught between the two crusts: the 1 and the highest number, a 6 on the small boards and a 9 on the large ones.

The clue is a length puzzle as much as a sum. A clue of 0 means the crusts sit side by side. A big clue forces them far apart with room between. Working out where the 1 and the highest number can sit is the heart of it, and the rest is ordinary sudoku.

How it plays

• Fill every cell so each row, column and box holds every number once.
• The crusts are the 1 and the highest number. Each edge clue sums the digits between them in that line.
• A clue of 0 means the two crusts are next to each other.
• Pick a number chip, tap a cell to place it, tap again to clear it.
• Notes pencils small candidates while you narrow a cell down.
• A finished line whose sum misses its clue glows. Stuck? Hint names the next step.

The difficulties

Easy is a six-wide grid that opens with most of its numbers already down, where a clue or two pins the crusts almost at once, half a minute of it. Medium keeps that six-wide grid but opens with ten to fifteen numbers, so the crusts do more of the work. Hard is the classic nine-wide, where placing the crusts and adding up the filling both pull their weight. Expert is nine-wide with fewer starting numbers than hard, and every board leans on the sandwich sum at least six separate times where hard needs it twice. You will not meet expert in a daily board; it waits for whenever you want the work. A fresh board is dealt every day, for nothing.

Nearby in the almanac: Digit, Skyit and Summit