题目 http://acm.hdu.edu.cn/showproblem.php?pid=6706 http://acm.hdu.edu.cn/showproblem.php?pid=6607 https://nanti.jisuanke.com/t/40522 https://nanti.jisuanke.com/t/A2003 https://nanti.jisuanke.com/t/39269 https://nanti.jisuanke.com/t/41390 https://blog.csdn.net/y_marcel_h/article/details/90225382 https://www.cnblogs.com/cjyyb/category/1124706.html