Killer Sudoku

Killer Sudoku follows normal sudoku rules — every row, column and 3×3 box holds 1 to 9 exactly once — but the grid is also divided into dotted cages. The small number in a cage's corner is the sum of its digits, and a digit can't repeat inside a cage.

• Select a square by tapping or with the arrow keys, then enter a digit with the keypad or keyboard.
• The line under the grid lists every combination that fits the selected cage, skipping combinations that clash with digits you've already placed.
• Notes (✎ / N / Shift+digit), Undo/Redo, Hint, Check and Pause work just like in Sudoku. Cages that add up wrong turn red when conflict highlighting is on.

Tips

Each row, column and box adds up to 45 — compare that with the cages inside it to find single squares ("the rule of 45"). Small cages are your friends: 3 in two cells must be 1+2, and 17 in two cells must be 8+9. Easy puzzles have small cages and a few given digits; Hard ones use cages of up to five cells.