@Override
    public boolean hasNext() {
        if (nextVal != null) {
            return true;
        }
        while (!stack.isEmpty()) {
            boolean pushedIntoStack = false;
            Iterator<NestedInteger> itr = stack.peek();
            if (itr.hasNext()) {
                NestedInteger ni = itr.next();
                if (ni.isInteger()) {
                    nextVal = ni.getInteger();
                    return true;
                } else {
                    pushedIntoStack = true;
                    stack.push(ni.getList().iterator());
                }
            }
            if (!pushedIntoStack) {
                stack.pop();
            }
        }
        return false;
    }
Date 04/17/2017
@author Tushar Roy

Given a nested list of integers, implement an iterator to flatten it.
Each element is either an integer, or a list -- whose elements may also be integers or other lists.
Example 1:
Given the list [[1,1],2,[1,1]],
By calling next repeatedly until hasNext returns false, the order of elements returned by next should be: [1,1,2,1,1].

https://leetcode.com/problems/flatten-nested-list-iterator/
src/com/interview/misc/NestedIterator.java