What is the lookup time complexity of HashSet(IEqualityComparer)?

Question

In C#.NET, I like using HashSets because of their supposed O(1) time complexity for lookups. If I have a large set of data that is going to be queried, I often prefer using

Answer 1

Lookup is still O(1) if you pass an IEqualityComparer. The hash set still uses the same logic as if you don't pass an IEqualityComparer; it just uses the IEqualityComparer's implementations of GetHashCode and Equals instead of the instance methods of System.Object (or the overrides provided by the object in question).