How to play

Killer Sudoku is Sudoku with nothing given. Every row, column and 3×3 box still takes the digits 1 through 9 exactly once, but the grid starts empty. Instead, dashed outlines divide it into cages, and the small number in a cage's corner is what its digits add up to. Inside one cage no digit repeats. Tap a cell, then tap a number to fill it in; the line under the board lists every way the selected cage can still be completed. Each puzzle here has exactly one solution, and none of them require guessing.

Controls

• Click or tap a cell, then a number — or type 1–9 directly
• ↑ ↓ ← → — move between cells
• N — toggle notes (pencil marks)
• Z or U — undo (unlimited)
• Delete, Backspace or 0 — erase a cell
• H — use a hint (3 per puzzle)
• R — restart the puzzle

Strategy tips

• Start with the cages that have one answer. Two cells adding to 3 are 1 and 2; two cells adding to 17 are 8 and 9; three cells adding to 6 are 1, 2 and 3, and three adding to 24 are 7, 8 and 9. Note those digits in and they ripple through their rows, columns and boxes.
• Use the 45 rule. Every row, column and box adds up to 45. If a box holds whole cages adding to 38 and one cell of a cage that sticks out, that cell is 7. Two rows make 90, three make 135 — the same trick, bigger.
• Read the cage line. Selecting any cell shows every combination its cage can still take. As digits go in, the list shrinks — when it is down to one combination, the cage is as good as solved.
• Then play Sudoku. Once the cages have seeded a few digits, the ordinary techniques take over: singles, pairs, locked candidates. A digit a cage must contain can be treated like a pointing pair against the cells that see all of it.

About Killer Sudoku

Killer Sudoku appeared in Japan in the 1990s under the name サムナンプレ ("sum number place"), crossing the arithmetic of Kakuro with the grid of Sudoku, and reached a wide audience when British newspapers took it up in 2005. The cages replace the given digits entirely: all the information is in the sums, which makes the opening slower and more mathematical than a classic Sudoku, and the finish just the same.

This edition ships 300 puzzles — 100 each of Easy, Medium and Hard. Every puzzle is proven to have a single solution and is graded by the techniques it needs: Easy falls to small-cage combinations, singles and the 45 rule on one row, column or box; Medium adds big cages, pairs, locked candidates and the 45 rule across two units; Hard calls for triples, X-wings and the 45 rule across three. Nothing ever requires trial and error.