Flatten a Nested List Iterator

Problem Given a nested list where each element is either an integer or another (arbitrarily deep) nested list, implement an iterator that returns the integers in order. Support next() (return the next integer) and hasNext() (whether one remains).

Input / Output

• Input: a nested list of integers, e.g. [[1,1],2,[1,1]].
• Output: integers streamed via next(): 1, 1, 2, 1, 1.

Constraints

• Nesting may be arbitrarily deep.
• Lists may be empty at any level; hasNext() must skip past empty sublists.

Example

• [[1,1],2,[1,1]] -> 1,1,2,1,1
• [1,[]] -> 1