meeting（类似树的直径问题，两次bfs或树形dp）
链接：https://ac.nowcoder.com/acm/contest/884/A来源：牛客网时间限制：C/C++ 1秒，其他语言2秒空间限制：C/C++ 524288K，其他语言1048576K64bit IO Format: %lld题目描述A new city has just been built. There'rennninteresting places...
