题目链接

扁平化嵌套列表迭代器

题目描述

注意点

• 每个元素要么是一个整数，要么是一个列表；该列表的元素也可能是整数或者是其他列表
• 嵌套列表中的整数值在范围 [-1000000, 1000000] 内
• NestedInteger中有三个方法，分别是：isInteger() ，判断当前存储的对象是否为 int；getInteger() , 如果当前存储的元素是 int 型的，那么返回当前的结果 int，否则调用会失败；getList() ，如果当前存储的元素是 List<‘NestedInteger’> 型的，那么返回该 List，否则调用会失败

解答思路

• 由于列表的元素也可能是整数或者是其他列表，所以先使用递归将迭代器中的列表都伸展开来加入到list中，其中list中的元素都是整数
• next和hasnext相当于遍历list的过程

代码

/*** // 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 empty list if this NestedInteger holds a single integer*     public List<NestedInteger> getList();* }*/
public class NestedIterator implements Iterator<Integer> {private List<Integer> list = new ArrayList<>();private int index;public NestedIterator(List<NestedInteger> nestedList) {add(nestedList);}private void add(List<NestedInteger> nestedList) {for (NestedInteger nestedInteger : nestedList) {if (nestedInteger.isInteger()) {list.add(nestedInteger.getInteger());} else {add(nestedInteger.getList());}}}@Overridepublic Integer next() {return list.get(index++);}@Overridepublic boolean hasNext() {return index < list.size();}
}/*** Your NestedIterator object will be instantiated and called as such:* NestedIterator i = new NestedIterator(nestedList);* while (i.hasNext()) v[f()] = i.next();*/

关键点

• 理解本题中NestedIterator和NestedInteger结构