[tialaramex]

if your hash table is a really good modern open addressed hash table, something like Google's Swiss Tables, you need a really good hash because you will be badly penalised otherwise, these modern structures demand a hash with proper behaviour for even halfway reasonable performance.

If it's just a My First Hash table with closed addressing, buckets etc. you needn't care too much. If you're hashing integers, just use the integer itself, that's a terrible "hash" but with this like 1980s data structure it's good enough.

[mtlmtlmtlmtl]

A lot of the time if the key is an int however you can get away with an array assuming the range is reasonably small.

Worth noting that for AOC I got by just fine with the simplest possible bucket based implementation.