341. Flatten Nested List Iterator展开多层数组

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:

Input: [[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: [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].

思路：Stack怎么写啊，可以不用stack吗？就是一个基本的NestedInteger遍历方法吧，知道有这回事就行 

整数也需要.getInteger()一下

public class NestedIterator implements Iterator<Integer> {
    LinkedList<Integer> flattenedList;
    Iterator<Integer> iterator;
    
    public NestedIterator(List<NestedInteger> nestedList) {
        flattenedList = new LinkedList<Integer>();
        flatten(nestedList);
        iterator = flattenedList.iterator();
    }
    
    public void flatten(List<NestedInteger> nestedList) {
        for (NestedInteger i : nestedList) {
            if (i.isInteger()) {
                flattenedList.add(i.getInteger());
            }else {
                flatten(i.getList());
            }
        }
    }

    @Override
    public Integer next() {
        //是返回itrator的next()
        return iterator.next();
    }

    @Override
    public boolean hasNext() {
        return iterator.hasNext();
    }
}