(This article was first published on

**Xi'an's Og » R**, and kindly contributed to R-bloggers)> printSudoku(z) +-------+-------+-------+ | 9 | | 7 5 | | 6 | | 9 | | 4 5 3 | 1 7 | 2 8 | +-------+-------+-------+ | 5 | 7 | 6 | | 1 9 | 6 8 | | | 8 | 3 | 1 | +-------+-------+-------+ | 7 2 | 5 9 | 4 | | | 2 | 6 7 | | | 6 | 2 | +-------+-------+-------+

**Y**esterday, I was finishing a sudoku grid in the metro and I ended up with four entries *a,b,b,a* that could be entered in two symmetric ways! Nothing mathematically surprising. However, this never happened to me before and, while it is obviously a possibility, I had not realised that sudoku creators could choose this option… This is not a well-defined question, but how likely is it that one ends up with such an exchange quadruplet (or rather pair of pairs)?! (The above was written using the sudoku R solver, pointed out there.)

Filed under: R, Statistics Tagged: R, sudoku

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