@Override
    public boolean hasNext() {
        while (currentList < vector.size() && vector.get(currentList).size() == 0) {
            currentList++;
        }
        return currentList < vector.size();
    }
Date 10/10/2016
@author Tushar Roy

Implement an iterator to flatten a 2d vector.

https://leetcode.com/problems/flatten-2d-vector/
src/com/interview/linklist/Flatten2DList.java