<p>You are given a nested list of integers <code>nestedList</code>. Each element is either an integer or a list whose elements may also be integers or other lists. Implement an iterator to flatten it.</p> <p>Implement the <code>NestedIterator</code> class:</p> <ul> <li><code>NestedIterator(List<NestedInteger> nestedList)</code> Initializes the iterator with the nested list <code>nestedList</code>.</li> <li><code>int next()</code> Returns the next integer in the nested list.</li> <li><code>boolean hasNext()</code> Returns <code>true</code> if there are still some integers in the nested list and <code>false</code> otherwise.</li> </ul> <p>Your code will be tested with the following pseudocode:</p> <pre> initialize iterator with nestedList res = [] while iterator.hasNext() append iterator.next() to the end of res return res </pre> <p>If <code>res</code> matches the expected flattened list, then your code will be judged as correct.</p> <p> </p> <p><strong>Example 1:</strong></p> <pre> <strong>Input:</strong> nestedList = [[1,1],2,[1,1]] <strong>Output:</strong> [1,1,2,1,1] <strong>Explanation:</strong> By calling next repeatedly until hasNext returns false, the order of elements returned by next should be: [1,1,2,1,1]. </pre> <p><strong>Example 2:</strong></p> <pre> <strong>Input:</strong> nestedList = [1,[4,[6]]] <strong>Output:</strong> [1,4,6] <strong>Explanation:</strong> By calling next repeatedly until hasNext returns false, the order of elements returned by next should be: [1,4,6]. </pre> <p> </p> <p><strong>Constraints:</strong></p> <ul> <li><code>1 <= nestedList.length <= 500</code></li> <li>The values of the integers in the nested list is in the range <code>[-10<sup>6</sup>, 10<sup>6</sup>]</code>.</li> </ul>