Comment by chowells
8 days ago
Please explain to me how you can hash n distinct strings into O(n) buckets in O(1) time. Please note that this process needs to work as n goes to infinity.
Hash tables are O(log n) structures when you don't hand-wave away the "compute a hash" part. The thing is, search trees are far worse than that in practice and you aren't hand-waving away the "compare two elements" part. That's where the real speed savings come from.
What I think you are saying is that computing the hash needs to process the entire string, and the length of that string roughly corresponds to log n, therefore it's O(log n). Not sure I am entirely convinced by that reasoning, but let's roll with it for now.
Because if you apply it to binary search, you need to compare the strings at every step, and by that logic, each of these operations is O(log n), which means your binary search is now O(log^2 n).
I guess the crux is that we are still comparing apples to oranges (or multiplication operations to comparison operations), and at the end what probably makes hashing faster is that we are not branching.
Still I don't think it makes sense to think of both hash tables and binary search as O(log n).