亚麻面试题：the biggest disadvantage of Hashmap

敢问这题怎么

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I would say its biggest disadvantage is more memory usage in order to achieve O(1). A hashmap has to maintain a low enough load factor in order to be effective, otherwise, the conflicts would be too high and it would be no longer O(1) but more towards O(n). Even under relatively high load factor, a bst would be considered better in resolving the conflicts than a list. Normally, when the load factor reaches to a preset level, a hashmap will need to extend its internal store and rehash.

hashmap需要pre allocate memory，memory用完了之后重新allocate memory会造成那个时间点的run time degradation.这在high performance要求的时候是不能接受的。
一般是跟BST比较。

Hashmap多线程环境下并发不安全？

有哈希冲撞？key non-ordered?

线程不安全吧

Thanks for sharing.

感谢分享和回答，学习了

TommyFox 发表于 2019-8-31 20:29
Hashmap多线程环境下并发不安全？

这个时候会被问java的Hashtable和hashmap的差别了

bitcpf 发表于 2019-9-1 00:21
hashmap需要pre allocate memory，memory用完了之后重新allocate memory会造成那个时间点的run time degrad ...

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