# Killer Sudoku Pro: spreadsheet helper

My dad called yesterday, leaving a voicemail informing me that he had a technical problem.  I returned the call, expecting to have to solve some form of driver compatibility issue or the like, but instead he gave me the following conundrum.

There is a variant of Sudoku called Killer Sudoku, in which areas of the grid, either square, rectangular or some other irregular shape, are caged off, a small number in the corner indicating the value to which the numbers therein must sum.  My dad informed me that there is a further variant (Killer Sudoku Pro) in which these cages are further marked to indicate whether the number in the corner represents the sum of the numbers therein, their product, or their subtraction.  (For subtraction, this is taken as the highest number minus all other numbers.)  There is also a divide operator, saved for the cages two squares in size—this equates to the higher number divided by the lower number. He asked whether there was a way to understand what options were valid in cages three-squares in size (squares are considered sufficiently basic for the human brain to fathom immediately) for each of the three valid operators.

I turned to Excel.  (No shit, Sherlock.)  And here is the result.  It’s a thing of beauty, if I may say so, the most poetic moment being when I established that the result of the minus operator could be established through the following formula:

(2 * MAX(cells)) – SUM(cells)

Hope you enjoy playing with it as much as I did creating it.