341. Flatten Nested List Iterator

You are given a nested list of integers nestedList. Each element is either an integer or a list whose elements may also be integers or other lists. Implement an iterator to flatten it. Implement the NestedIterator class: - NestedIterator(List<NestedInteger> nestedList) Initializes the iterator with the nested list nestedList. - int next() Returns the next integer in the nested list. - boolean