Hash Table embarrassment

Due to the cache hit rate, the performance of the hash table is generally better than that of the Red/black tree. Even if there are only 32 elements, 5 random memory accesses are required. Random memory access is unfriendly to CPU cache. The biggest drawback of a hash table is that when the data volume is difficult to estimate, you cannot set a suitable bucket. The number of elements may be 10 or 10000. Here are several ideas: 1. set the default bucket value to around 100, and then enable automatic expansion of the hash table. The disadvantage is that the performance is affected during expansion. 2. Combined with the business, each time 10000 buckets are provided, the disadvantage is that the memory is wasted and cannot be processed in extreme situations such as million. 3. Convert the list of hash tables into hash tables. The disadvantage is that the structure is complex and the hash speed is slow for multiple times. Overall, solution 1 is better.