Killer Sudoku

Killer Sudoku's first appearance in the UK was in 'The Times', in 2005 and this newspaper is responsible for the tasteless nomenclature. The puzzle was the brainchild of Miyuki Nisawa, a pupil of Japanese puzzle master, Tetsuya Nishio.

A felicitous conjunction of Sudoku and Kakuro. All Sudoku rules apply, but the normal Sudoku grid is overlaid with an irregular mosaic of cages. The sum of the digits placed in each cage must equal the small number in the top corner of each cage.

The strategies that are employed to solve Sudoku and Kakuro can be used for this puzzle, separately and in combination – and an understanding of the underlying principles can be particularly valuable. For example, the 45 rule – the fact that 1-9 must fit in a row, column or nonet (3x3 sector) means that the sum of digits in each must equal 45 (1+2+3, etc). If the cages are all confined within a nonet, row or column, the digits in the cages will equal 45. If one of the cages extends beyond the region by one cell, the digit in that cell will equal the sum of the cages in the region minus 45.