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Upside-down

 
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codebreaker



Joined: 26 Mar 2006
Posts: 1

PostPosted: Sun Mar 26, 2006 8:28 am    Post subject: Upside-down Reply with quote

I have noticed that all the Sudokus I have seen so far have numbers in the same location when the puzzle is turned upside-down. Allthough the numbers are different, their location on the grid is identical. This holds true for the Pappocom puzzles I have been doing in the Toronto Star newspaper and also for a book I have containing 300 Sudokus. Can someone tell me why this is the case? I have found Sudokus easier to solve if I work on the corresponding boxes first, i.e. the lower right box corresponds to the upper left, and so on.
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TKiel



Joined: 22 Feb 2006
Posts: 292
Location: Kalamazoo, MI

PostPosted: Wed Mar 29, 2006 1:39 pm    Post subject: Reply with quote

It's called symmetry and while there are many different kinds, most Sudoku puzzles use (I think) 180 degree rotational. It's not necessary for a puzzle to be symmetrical for it to be valid, but when entering a starting grid manually it makes it easier to catch either omitted or misplaced numbers. It's an additional constraint that some puzzle setters impose on themselves, plus the initial clue set can have an interesting look to it.
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David Bryant



Joined: 29 Jul 2005
Posts: 559
Location: Denver, Colorado

PostPosted: Wed Mar 29, 2006 4:10 pm    Post subject: Crosswords are also symmetrical Reply with quote

There's also the fact that crossword puzzles are traditionally constructed with 2-fold rotational symmetry, so puzzle editors are used to seeing such patterns. dcb
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