What are the rules of sumdoku?
On first inspection, the sumdoku puzzle may look a little like killer sudoku. However, there are some real differences, both to the rules and the visual presentation.
Whilst with killer sudoku dotted cages will generally be used for black and white display of the puzzle, with sumdoku, this is replaced with solid black cages for each cell (which is possible because the box regions are removed, as explained further down).
The extension to the cages of killer sudoku is that the sum may require subtraction, division or multiplication and not just addition. There are a couple of other changes, too. The box regions of killer sudoku are gone, and so the numbers just have to be placed once per row and column.
The other significant change is that repetition is allowed within a cage, whereas of course in puzzles like killer sudoku or kakuro that is never allowed.
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