341 - Flatten Nested List Iterator.

Medium

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 <code>-10⁶, 10⁶</code>.