LeetCode #341 - Flatten Nested List Iterator_iteratorlistfile函数作用-优快云博客

本文链接：https://blog.youkuaiyun.com/LawFile/article/details/81215897

本文介绍了一种实现套叠链表迭代器的方法，通过使用栈来存储链表元素，确保能够正确地按顺序返回扁平化后的链表元素。关键在于hasNext函数的实现，它能确保每次调用都能确定是否存在下一个元素。

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题目描述：

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].

套叠链表的定义如下：
* class NestedInteger {
* public:
* // Return true if this NestedInteger holds a single integer, rather than a nested list.
* bool isInteger() const;
*
* // Return the single integer that this NestedInteger holds, if it holds a single integer
* // The result is undefined if this NestedInteger holds a nested list
* int getInteger() const;
*
* // Return the nested list that this NestedInteger holds, if it holds a nested list
* // The result is undefined if this NestedInteger holds a single integer
* const vector<NestedInteger> &getList() const;
* };
这道题的关键在hasNext函数，它需要每次遍历都能够确定是否还有下一个元素，由于采用栈存储套叠链表元素，所以如果发现栈顶元素不是数字，我们需要将这个套叠链表分解，也就是将链表中的所有元素反向压栈，接着再判断栈顶是否为数字，如果还不是，又接着将链表元素反向压栈，这样不断循环。

class NestedIterator {
public:
    NestedIterator(vector<NestedInteger> &nestedList) {
        for(int i=nestedList.size()-1;i>=0;i--)
            s.push(nestedList[i]);
    }

    int next() {
        int result=s.top().getInteger();
        s.pop();
        return result;
    }

    bool hasNext() {
        while(!s.empty())
        {
            NestedInteger x=s.top();
            if(x.isInteger()) return true;
            vector<NestedInteger> v=x.getList();
            s.pop();
            for(int i=v.size()-1;i>=0;i--) s.push(v[i]);
        }
        return false;
    }

private:
    stack<NestedInteger> s;
};

/**
 * Your NestedIterator object will be instantiated and called as such:
 * NestedIterator i(nestedList);
 * while (i.hasNext()) cout << i.next();
 */