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 hasNext()` Returns `true` if there are still some integers in the nested list and `false` otherwise. Your code will be tested with the following pseudocode: initialize iterator with nestedList res = [] while iterator.hasNext() append iterator.next() to the end of res return res ``` If `res` matches the expected flattened list, then your code will be judged as correct.   **Example 1:** **Input:** nestedList = [[1,1],2,[1,1]] **Output:** [1,1,2,1,1] **Explanation:** By calling next repeatedly until hasNext returns false, the order of elements returned by next should be: [1,1,2,1,1]. ``` **Example 2:** **Input:** nestedList = [1,[4,[6]]] **Output:** [1,4,6] **Explanation:** By calling next repeatedly until hasNext returns false, the order of elements returned by next should be: [1,4,6]. ```   **Constraints:** - `1 <= nestedList.length <= 500` - The values of the integers in the nested list is in the range `[-106, 106]`.