Solution to a6e7: Int set iterators
See code at solutions/code/tutorialquestions/questiona6e7
The way iterators can be implemented for this question are exactly analogous to the methods demonstrated in the solution to question 1486. Again, I have provided three versions using standard classes, inner classes and anonymous inner classes.
The interesting parts of this question are Steps 3 and 4. Look at the AbstractIntSet class (in any of the solution versions)
to see that the iterator facilities provided by an IntSet allow us to implement algorithms to check containment, remove one set from another, add
one set to another, and turn a set into a string, at the abstract level. We do not need to implement separate algorithms for MemoryEfficientIntSet
and SpeedEfficientIntSet.