Throws:;; The function has no effect if an exception is thrown, unless it is thrown by the container's hash function or comparison function.
Throws:;; The function has no effect if an exception is thrown, unless it is thrown by the container's hash function or comparison function.当 `size() == 0` 时, `rehash(0)` 将释放底层桶数组。
Throws:;; The function has no effect if an exception is thrown, unless it is thrown by the container's hash function or comparison function.当 `size() == 0` 时, `rehash(0)` 将释放底层桶数组。