Killer Sudoku


If the milk delivery problem looks familiar to newspaper readers, then perhaps it really is. Killer Sudoku is an advanced version of the popular Sudoku puzzle. In Killer Sudoku, as in Sudoku, the player is asked to place the numbers one to nine in a grid with each number occurring once and once in each row and column. However, rather than giving the player some starting numbers as in Sudoku, Killer Sudoku tells how the numbers add up in certain combinations. This is precisely the same as the milk delivery problem.

A very similar puzzle is called Griddler, where the player is given a square grid and told how many black squares there are in each row and column, along with some extra information about how they are grouped. Solving a Griddler problem is another exercise in tomography. Usually we solve Sudoku and Griddler problems in the newspapers by using a pencil, eraser, and a bit of luckand judgment. However we will describe a computer algorithm to solve even more general problems.

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