Kakuro, also known as cross sums, is a number logic puzzle. Black clue cells hold a sum for the white run to their right, shown as the top number, or the run below, shown as the bottom number. Fill every white cell with a digit from 1 to 9 so that each run adds up to its clue, with no digit repeated in a run. Every grid has one answer, reachable by logic.
Tap a cell, then a digit, or type it. Notes mode pencils in candidates. Tap a clue to list every digit combination for its sum, with clashing ones struck out. A repeated digit turns red, and so does a clue whose sum can no longer be made. A finished run shows a green tick on its clue.
No hints and no mistakes earns three stars; one or two mistakes give two, and a hint caps you at two. The hint fixes a wrong digit first, otherwise places or narrows the next cell and says why. Sixty grids run across five tiers, from First Sums to Grand Grids, with later tiers asking for new techniques, plus a daily grid.
Worked example
A cell sits where an across run of two cells totalling 3 meets a down run of two cells totalling 4. The only way to make 3 from two different digits is 1 + 2, and 4 is 1 + 3. The only digit in both is 1, so the cell is 1. Then 2 goes across and 3 down.
Strategy tips
Learn the fixed sums. 3 and 4 in two cells, 16 and 17 in two, 6 and 7 in three, and 23 and 24 in three each have only one set of digits.
Find must-have digits. A digit that every combination needs must go in the only cell that can take it.
Use pairs. Two cells limited to the same two digits keep those digits out of the rest of the run.