用陣列時會

Segmentation fault (core dumped)
用vector時是

terminate called after throwing an instance of 'std::bad_alloc'
  what():  std::bad_alloc
Aborted (core dumped)

用vector時先預留空間

vec.reserve(n);//n為預留的大小
可以參考:https://zhuanlan.zhihu.com/p/361331817