Killer Sudoku combines classic Sudoku with simple arithmetic. The usual 1-through-9 rules still apply: every row, column, and 3×3 box holds each digit exactly once.

On top of that, the grid is divided into dotted cages, each labelled with a target sum. The digits inside a cage must add up to that sum — and no digit can repeat inside a single cage.

Start by scanning small cages (2–3 cells) where the possible combinations are limited. A cage sum of 3 across two cells must be 1+2, for example. Cross-reference those candidates against the row, column, and box constraints to lock in certain placements.

Expert puzzles demand advanced techniques: swordfish, XY-wing chains, unique rectangles. A correct solve at this level rewards patience more than speed.

The timer is for you, not for us. Fewer than twenty minutes on an expert puzzle is very good; under ten is exceptional.