Why is accessing an element of a dictionary by key O(1) even though the hash function may not be O(1)?

Question

I see how you can access your collection by key. However, the hash function itself has a lot of operations behind the scenes, doesn\'t it?

Assuming you have a nice h

Answer 1

from the docs:

Retrieving a value by using its key is very fast, close to O(1), because the T:System.Collections.Generic.Dictionary`2 class is implemented as a hash table.

So it can be O(1) but might be slower. Here you can find another thread regarding hashtable performance: Hash table - why is it faster than arrays?