Toroidal: Tough To Get Your Head AroundToroidal sudoku it is safe to say is a version you will almost certainly have never seen in print. That's because it is considered too tough and tricky to solve by many. And also because hardly anyone makes this particular variant sudoku puzzle!
Although the rules are still the same as normal sudoku: place the numbers once in each region of the puzzle, because some regions wrap around the edges of the grid (think pacman walking off one side and coming back on the other side of the screen), they can be very hard to solve.
Keeping track of which cells are in which regions is one cause of trickery (often alleviated by using colour) but secondly is the fact it is hard to keep track of values in regions where the cells can be in such different parts of the grids yet affect each other. For instance if you look at the sample grid to the right, you'll see the light-green region at the top left of the puzzle wraps around to the final cell in row one and also to a set of three cells at the bottom right of the grid.
The key to solving toroidal sudoku is conscientously updating pencilmarks in each cell within a toroidal region each time you make a placement: failure to do this even once can lead to much frustration; with good accounting of your deductions then the puzzle becomes much more readily solvable! But it's not for the faint-hearted.
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Last updated: 20 Feb 2012
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