The most difficult Sudoku in the world, it has only “one answer”
Finnish mathematician Yinka La spent three months in the design of a Sudoku (squared game), which claimed to be by far the most difficult in the world, and it has only one answer. But earlier this year a 69-year-old Chinese farmer, Huang Jinlong, provided a second answer in just three days. Huang Jinlong also said he wanted to make more friends with interests on Sudoku.
Source: Xinhua Net