The History of Killer Sudoku
Sudoku meets the sums of Kakuro: a variant that trades given digits for arithmetic.
Sums on a Sudoku Grid
Puzzles that combine Sudoku's rules with cage sums were already printed in Japan in the 1990s, where sum puzzles such as Kakuro were popular. The idea spread widely in 2005, when British newspapers began running such puzzles under the name Killer Sudoku during the worldwide Sudoku boom.
The name is descriptive, not a brand: 'killer' simply promised a harder challenge than an ordinary Sudoku, since there are few or no digits to start from.
How the Puzzles Here Are Made
Every Killer Sudoku here starts as a freshly generated, completely solved Sudoku grid, which is then cut into connected cages without a repeated digit in any cage.
A built-in solver then checks whether the cage sums allow only one solution. If not, a digit where two possible solutions differ is revealed as a given, and the check repeats until exactly one solution remains.
A Note on the Names
The names 数独 (Sudoku), カックロ (Kakuro) and スリザーリンク (Slitherlink) are registered trademarks of the publisher Nikoli in Japan, and 橋をかけろ (Hashiwokakero) is the name under which Nikoli publishes that puzzle. PaperGames is not affiliated with Nikoli, is not endorsed or reviewed by Nikoli, and therefore uses other names in its Japanese version. The puzzle types themselves are free; every puzzle here is generated fresh on the device.