线段树+树的直径：
https://github.com/YANGRUZHAO/ACM/blob/master/%E6%95%B0%E6%8D%AE%E7%BB%93%E6%9E%84/%E6%89%AB%E6%8F%8F%E7%BA%BF(%E5%A4%9A%E4%B8%AA%E7%9F%A9%E9%98%B5%E8%A6%86%E7%9B%96%E7%9A%84%E5%92%8Chdu1255).cpp
https://github.com/YANGRUZHAO/ACM/blob/master/%E6%95%B0%E6%8D%AE%E7%BB%93%E6%9E%84/%E6%A0%91%E7%9A%84%E7%9B%B4%E5%BE%84(%E8%AE%A1%E7%AE%97%E6%A0%91%E7%9A%84%E6%AF%8F%E4%B8%AA%E7%82%B9%E5%87%BA%E5%8F%91%E7%BB%8F%E8%BF%87%E6%89%80%E6%9C%89%E7%82%B9%E4%B8%8D%E8%BF%94%E5%9B%9E%E8%B5%B7%E7%82%B9%E7%9A%84%E6%9C%80%E7%9F%AD%E8%B7%AF%E5%BE%84).cpp
网络流：
https://github.com/YANGRUZHAO/ACM/blob/master/%E6%95%B0%E6%8D%AE%E7%BB%93%E6%9E%84/%E6%9C%80%E5%A4%A7%E8%B4%B9%E7%94%A8%E6%B5%81%E8%BE%93%E5%87%BA%E9%80%89%E6%8B%A9%E8%B7%AF%E5%BE%84%E9%97%AE%E9%A2%98(%E8%88%AA%E7%A9%BA%E8%B7%AF%E7%BA%BFp2770).cpp
https://github.com/YANGRUZHAO/ACM/blob/master/%E6%95%B0%E6%8D%AE%E7%BB%93%E6%9E%84/%E6%9C%80%E5%B0%8F%E5%89%B2(hdu4289).cpp
https://github.com/YANGRUZHAO/ACM/blob/master/%E6%95%B0%E6%8D%AE%E7%BB%93%E6%9E%84/%E6%9C%80%E5%B0%8F%E5%89%B2(%E7%BD%91%E6%A0%BC%E5%8F%96%E6%95%B0p2774).cpp
https://github.com/YANGRUZHAO/ACM/blob/master/%E6%95%B0%E6%8D%AE%E7%BB%93%E6%9E%84/%E6%9C%80%E5%B0%8F%E5%89%B2(%E9%AA%91%E5%A3%AB%E5%85%B1%E5%AD%98p3355).cpp
https://github.com/YANGRUZHAO/ACM/blob/master/%E6%95%B0%E6%8D%AE%E7%BB%93%E6%9E%84/%E6%9C%80%E5%B0%8F%E6%9C%80%E5%A4%A7%E8%B4%B9%E7%94%A8%E6%B5%81(%E8%BF%90%E8%BE%93%E9%97%AE%E9%A2%98p4015).cpp
https://github.com/YANGRUZHAO/ACM/blob/master/%E6%95%B0%E6%8D%AE%E7%BB%93%E6%9E%84/%E6%9C%80%E5%B0%8F%E8%B4%B9%E7%94%A8%E6%9C%80%E5%A4%A7%E6%B5%81(poj2195).cpp
https://github.com/YANGRUZHAO/ACM/blob/master/%E6%95%B0%E6%8D%AE%E7%BB%93%E6%9E%84/%E8%B4%B9%E7%94%A8%E6%B5%81(%E6%95%B0%E5%AD%97%E6%A2%AF%E5%BD%A2p4013).cpp
