https://github.com/Wowkiee/ACM-ICPC/blob/master/Luogu/2444.cpp https://github.com/Wowkiee/ACM-ICPC/blob/master/Zoj/3784.cpp
Luogu 2444 [POI2000]病毒 & Zoj 3784
原文：https://www.cnblogs.com/wuyuanyuan/p/9087549.html
