Flatten Nested List Iterator

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#leetcode #队列 #数据结构

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本文介绍了一种使用队列实现的嵌套列表迭代器，该迭代器可以将嵌套的整数列表扁平化，并按顺序返回所有元素。通过递归地检查每个元素并将其放入队列中，确保了元素的正确输出顺序。

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:
Given the list [[1,1],2,[1,1]],

By calling next repeatedly until hasNext returns false, the order of elements returned by next should be: [1,1,2,1,1].

Example 2:
Given the list [1,[4,[6]]],

By calling next repeatedly until hasNext returns false, the order of elements returned by next should be: [1,4,6].

这个题不难，有想法就好实现，用队列来解决。

/**
 * // This is the interface that allows for creating nested lists.
 * // You should not implement it, or speculate about its implementation
 * public interface NestedInteger {
 *
 *     // @return true if this NestedInteger holds a single integer, rather than a nested list.
 *     public boolean isInteger();
 *
 *     // @return the single integer that this NestedInteger holds, if it holds a single integer
 *     // Return null if this NestedInteger holds a nested list
 *     public Integer getInteger();
 *
 *     // @return the nested list that this NestedInteger holds, if it holds a nested list
 *     // Return null if this NestedInteger holds a single integer
 *     public List<NestedInteger> getList();
 * }
 */
public class NestedIterator implements Iterator<Integer> {

    Deque<Integer> queue=new ArrayDeque<Integer>();
	
	public void putIntoQueue(List<NestedInteger> list){
		for(int i=0;i<list.size();i++){
			if(list.get(i).isInteger()){
				queue.offer(list.get(i).getInteger());
			}else{
				putIntoQueue(list.get(i).getList());
			}
		}
	}
	
	public NestedIterator(List<NestedInteger> nestedList) {
		putIntoQueue(nestedList);
    }

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

    public boolean hasNext() {
    	return queue.size()>0;
    }
}

/**
 * Your NestedIterator object will be instantiated and called as such:
 * NestedIterator i = new NestedIterator(nestedList);
 * while (i.hasNext()) v[f()] = i.next();
 */