HashSet versus Dictionary<T, K> w.r.t searching time to find if an item exists

Question

HashSet<T> t = new HashSet<T>();
// add 10 million items


Dictionary<T, K> t = new Dictionary<T, K>();
// add 10 million items.

Whose .Contains method will return quicker?

Just to clarify, my requirement is I have 10 million objects (well, strings really) that I need to check if they exist in the Data Structure. I will NEVER iterate.

Answer 1

I assume you mean Dictionary<TKey, TValue> in the second case? HashTable is a non-generic class.

You should choose the right collection for the job based on your actual requirements. Do you actually want to map each key to a value? If so, use Dictionary<,>. If you only care about it as a set, use HashSet<>.

Answer 2

These are different data structures. Also there is no generic version of HashTable.

HashSet contains values of type T which HashTable (or Dictionary) contains key-value pairs. So you should choose collection on what data you need to be stored.