[leetcode]341. Flatten Nested List Iterator展开嵌套列表的迭代器

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].

题目

将Nested List展平，像访问一个一维列表一样访问嵌套列表。

思路

queue

代码

public class NestedIterator implements Iterator<Integer> {
    
    Queue<Integer> queue;
    
    public NestedIterator(List<NestedInteger> nestedList) {
       queue = new LinkedList<>();
       helper(nestedList); 
    }

    @Override
    public Integer next() {
        return queue.poll();
    }

    @Override
    public boolean hasNext() {
        return !queue.isEmpty();
    }
    private void helper(List<NestedInteger> nestedList){
        for(NestedInteger n:nestedList){
            if(n.isInteger()){
                queue.add(n.getInteger());
            }else{
                helper(n.getList());
            }
        }
    }
}