扩展欧几里得算法（转载）（扩欧）

https://blog.csdn.net/zhjchengfeng5/article/details/7786595?ops_request_misc=%257B%2522request%255Fid%2522%253A%2522165149606016782184659454%2522%252C%2522scm%2522%253A%252220140713.130102334..%2522%257D&request_id=165149606016782184659454&biz_id=0&utm_medium=distribute.pc_search_result.none-task-blog-2~all~top_positive~default-1-7786595.142^v9^control,157^v4^control&utm_term=%E6%89%A9%E5%B1%95%E6%AC%A7%E5%87%A0%E9%87%8C%E5%BE%97%E7%AE%97%E6%B3%95&spm=1018.2226.3001.4187