一套持久化平衡树，可用于代替sgiSTL中的rope，且功能更加强大（略作修改可实现持久化动态树）使用GNUC++标准（在OI前辈fanhq指导下完成）文件内自带使用方法样例-A persistent balanced BST, can be used instead of rope in sgiSTL, and more powerful (slightly modified to achieve lasting dynamic tree) (OI seniors fanhq completed under the guidance) comes with sample files to use within