Write a method named addAll that could be placed inside the HashSet2 class.
This method accepts another HashSet2 as a parameter and adds all elements from that set into the current set, if they are not already present.
For example, if a set s1 contains [a, b, c] and another set s2 contains [a, x, c, z], the call of s1.addAll(s2); would change s1 to store [a, b, c, x, z] in some order.
You are allowed to call methods on your set and/or the other set.
Do not modify the set passed in.
This method should run in O(N) time where N is the number of elements in the parameter set passed in.
(NOTE: To be compatible with our site and avoid conflicting with Java's java.util.HashSet, our HashSet is renamed HashSet2 here.)
