A Finnish mathematician has created what he calls the world's toughest sudoku -- a puzzle that took three months to create and has just one solution.
The puzzle was created by scientist and mathematician Arto Inkala, who reportedly compiles sudokus for fun in his spare time. He had created what he called the world's toughest puzzle four years ago. This one is even more challenging, he claims.
"Some people might make three or four lucky guesses and so be able to solve it in 15 minutes or half an hour and will wonder why it is said to be so difficult," he said. "But it will normally take days to solve by logic."
The puzzle was commissioned by Efamol, a manufacturer of omega-3 supplements that the company sells as brain-power-boosting supplements, and was generated by a computer program written by Inkala.
In sudoku, a nine-by-nine grid is divided into three-by-three blocks; the puzzle solver aims to fill a digit into each box such that each row, column, and three-by-three block contains each of the digits 1 through 9 exactly once.
Twenty-three of the 81 squares in Inkala's super sukodku are already filled in. Removing even one of these numbers would have vastly increased the number of possible solutions, making it easier to solve by luck alone.
So the puzzle's difficulty -- and frustration factor -- lies in the number of mental leaps needed to complete each square.