Implement an iterator to flatten a 2d vector.
For example,
Given 2d vector =
[ [1,2], [3], [4,5,6] ]
By calling next repeatedly until hasNext returns false, the order of elements returned by next should be: [1,2,3,4,5,6]
.
Follow up:
As an added challenge, try to code it using only iterators in C++ or iterators in Java.