update写错了，而且显然是没搞懂线段树，建议重看
by smallpeter @ 2023-02-07 13:43:16
注意审题，是加上val不是改成val
by roarer @ 2023-02-07 14:07:31
@[roarer](/user/675711) AC力，Thanks♪(･ω･)ﾉ
by WD2c0mP @ 2023-02-07 14:41:10