The Doppit Almanac · No. 40

Addit

Fill the runs so each adds up to its clue

What it is

Addit is Kakuro, a crossword made of sums. The grid is black cells and white ones, and every straight line of white cells is a run. Each run carries a clue in the black cell where it starts: an across clue above a diagonal, a down clue below it. Fill the white cells with the digits 1 to 9 so every run adds up to its clue.

One rule makes it a puzzle rather than arithmetic. No digit may be used twice inside a run, which turns a clue into a small set of digit combinations. Two cells adding to 17 can only be 8 and 9. Three adding to 23 can only be 6, 8 and 9. Every white cell sits in an across run and a down run at once, and the digit it takes has to suit both.

How it plays

• Fill every white cell with a digit from 1 to 9.
• Each run adds up to the clue in the black cell where it starts.
• A clue above the diagonal is for the run going across, one below it for the run going down.
• No digit is used twice inside the same run.
• Tap a digit, then tap a cell to write it. Tap a filled cell to clear it.
• Notes writes small digits instead, for digits you have not settled on. Stuck? Hint names the next forced digit and says why.

The difficulties

Easy is six white cells in a block two by three, about half a minute of reading a cell's two clues against each other. Medium keeps the four by four grid, runs to nine white cells and takes about fifty seconds. Hard is six by six, where a cell's two runs allow different digits often enough that you work the crossings rather than the runs. Expert is eight by eight with runs up to five cells long, and every board asks you at least twice to assume a digit, follow it a few moves, and find a run left with no digit it can take. A fresh board is dealt every day, for nothing.

Nearby in the almanac: Plotit, Summit and Digit