341. 扁平化嵌套列表迭代器

341. 扁平化嵌套列表迭代器

第一次在类里面使用递归

答案中将原vector展开存储后再取数值不符合迭代器的思想，因此实现了一个在原数组上进行操作的迭代器

/**
 * // This is the interface that allows for creating nested lists.
 * // You should not implement it, or speculate about its implementation
 * 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;
 * };
 */

class NestedIterator {
public:
    NestedIterator(vector<NestedInteger> &nestedList) : list(nestedList), cur(list.begin()) {

    }

    int next() {
        if(cur->isInteger())
            return (cur++)->getInteger();
        else
            return it->next();
    }
    
    bool hasNext() {
        // while的作用是去除空list防止误导
        while(cur != list.end())
        {
            if(cur->isInteger())
                return true;
            if(!it)
                it = std::make_shared<NestedIterator>(cur->getList());
            if(!it->hasNext())
            {
                ++cur;
                it = nullptr;
            }
            else
                return true;
        }
        return cur != list.end();
    }
private:
    vector<NestedInteger>& list;
    vector<NestedInteger>::iterator cur;
    std::shared_ptr<NestedIterator> it = nullptr;
};

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