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The world’s most difficult sudoku puzzle

Finnish mathematician Arto Inkala recently claimed to have created the world’s hardest Sudoku puzzle. Based on the number of deductions that need to be made to fill in a single cell, this puzzle achieves a difficulty rating of 11 stars, compared with five stars for the average newspaper sudoku.

Can you crack it? Have a go.

If you get stuck — or rather, when you get stuck — just paste the following grid into Bill DuPree’s sudoku solver, which will solve it for you in a fraction of a second. Thanks, Bill!

8 . . . . . . . .
. . 3 6 . . . . .
. 7 . . 9 . 2 . .
. 5 . . . 7 . . .
. . . . 4 5 7 . .
. . . 1 . . . 3 .
. . 1 . . . . 6 8
. . 8 5 . . . 1 .
. 9 . . . . 4 . .

Incidentally, if you install Bill’s software on your own computer, you’ll notice that it includes an option for calculating the difficulty of a sudoku puzzle. Typical values range from 80 or less for easy puzzles, up to 761 and above for “diabolical” puzzles. Arto’s puzzle achieves a thoroughly impressive score of 187,090.

(via telegraph.co.uk)

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