I need to keep track of all states previously visited in a game in C#. A state is a list of integers. Some examples of states are:

List state1 = new List(){1,2,3}

List state2 = new List(){1,3,5}

List state3 = new List(){1,2,3}

My assignment is to use a hash table to determine whether a state has been visited. Can you please describe (using C#) how I can create, add states to and check whether a list has been added to a hash table? For example, assume state1 was added to the hash table. Then I need a function that tells me that state3 can not be added to the hash table because the same sort of list (1,2,3) has been added before.