As performance of this search will be a problem, you will need to use the algorithm with the

*computational time complexity*of the search asymptotically does not depend on the size of actual collection. Just in your case, use

`System.Collections.Generic.HashSet<T>`

:http://msdn.microsoft.com/en-us/library/bb359438.aspx[^],

http://msdn.microsoft.com/en-us/library/bb356440.aspx[^],

http://msdn.microsoft.com/en-us/library/bb353005.aspx[^].

(I also referenced about two methods you will need to use in your simple case, to add and check up the value.)

It will give you the computational complexity of

**O(1)**. To understand it, please see also:

http://en.wikipedia.org/wiki/Big_O_notation[^],

http://en.wikipedia.org/wiki/Time_complexity[^].