https://www.luogu.org/blog/returntime/qian-tan-su-shuo-shai-you-hua 素数筛优化 https://www.cnblogs.com/fnlingnzb-learner/p/9374732.html 排序相关 https://blog.csdn.net/heimu24/article/details/81189700 mkd进阶 http://codeforces.com/blog/entry/61587 随机数生成