@[NM_ljy](/user/688783) add1写的有问题，左右儿子的区间长度不一定是直接除二。
by Killer_joke @ 2023-05-14 22:00:26
@[Killer_joke](/user/915814) thx,+已A
~~我在改以前用树状数组写的**代码~~
by SilverLi @ 2023-05-14 22:03:38