HashSet<T> is a generic class which contains an unordered collection of elements.
The elements are stored using their hashcodes, thus it provides faster speed for Collection standard
methods include Remove, Contains etc.
HashSet<int> hs = new HashSet<int>();
Loop through a HashSet:
foreach (int i in hs)
is a class similar to the hashmap in other languages. It contains a collection of key value pairs,
and provides faster methods include Remove, Contains etc.
Hashtable ht = new Hashtable();
Loop through a Hashtable:
for (string ky in hs.Keys)
int val = hs[key];