As of 20 1 1 year, the number of prompts found in 9×9 standard Sudoku is at least 17, and the deadline for editing this item is (201.1.. * * * Unequal 17 is found, suggesting that the puzzle is 49 15 1, and the number is still rising slowly. If you find the 17 puzzle first, you can upload it to the "17 Sudoku Verification" website. Of course, you can also download this 49 17 here.
Whether there is a qualified prompt number 16 has also been debated for a long time on the internet. Someone found the double solution of 16 hint number, but still did not find the unique solution. Some foreign netizens have given proof of why at least 17 prompt is needed, which has been questioned by everyone. For example, the minimum number of prompts for 9×9 diagonal Sudoku (based on the standard Sudoku rule, two diagonal numbers are not repeated) is 12, and according to his theory, more prompts are needed.
In addition, in 2006, Gary McGuire[2] wrote a program, trying to prove the existence of Sudoku prompted by 16 by violence. The method is simple. Since bertram felgenhauer and Fraser Jarvis have calculated that the total number of non-equivalent disks is 5,472,730,538, run the prompt for each case where the final disk is 16. But because it is a violent method, it takes 300 thousand years for a single-core computer to run. Professor Wu Yicheng of Taiwan Province Province and his team improved Gary McGuire's program, which greatly improved the efficiency. The calculation can be completed in about 24 17 years. And put it on BOINC (Berkeley Open Network Computing Platform), and let the computers all over the world join BOINC to calculate together. Fortunately, by the time this entry was edited (20 12 04 18), 51.73% had been completed [3].
Gary McGuire's team designed a new algorithm in 2009. Using the idea of death mode, it took 765,438+million hours of CPU time. On 2065,438+02, 1, 1 6, it was proved that there was no unique solution for 9×9 standard sudoku, and then it was explained that at least 65,438+was needed. And in 2009, they updated the source code of their papers and web pages.