QuietdokuHow to solve killer sudoku
Killer sudoku mixes sudoku with a little arithmetic. Here are the rules, a chart of every cage combination, and the first three tricks to learn.
The rules
- Fill the 9×9 grid so every row, column and 3×3 box contains 1–9 exactly once.
- The digits in each dashed cage add up to the small number in its corner.
- A digit cannot repeat within a cage.
Most killer puzzles start with an empty grid: the cage sums are the only clues. A well-made puzzle has exactly one solution and never needs guessing.
Three tricks that solve most puzzles
Unique combinations
Some sums can only be made one way. A 2-cell cage of 3 is always 1+2, of 4 always 1+3, of 16 always 7+9, of 17 always 8+9. A 3-cell cage of 6 is always 1+2+3 and of 24 always 7+8+9. Start there.
The rule of 45
Every row, column and box contains 1–9, which add up to 45. Add up the cages that sit completely inside a row; whatever is missing from 45 belongs to the cells that poke out of it. One leftover cell means you know its digit.
Cages inside a box
If a cage must contain a digit (for example a 2-cell cage of 3 must contain 1) and the whole cage sits in one row, column or box, no other cell there can hold that digit.