[leetcode]341. Flatten Nested List Iterator

题目链接：https://leetcode.com/PRoblems/flatten-nested-list-iterator/?tab=Description

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].

/** * // 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)    {        vector<int> res;        for(int i=0;i<nestedList.size();i++)            flatten(nestedList[i]);        k=0;    }    int next()    {        return flat[k++];    }    bool hasNext()    {        return k<flat.size();    }private:    vector<NestedInteger> vec;    vector<int> flat;    int k=0;    void flatten(NestedInteger n)    {        if(n.isInteger())        {            flat.push_back(n.getInteger());            return;        }        const vector<NestedInteger> v=n.getList();        for(int i=0;i<v.size();i++)            flatten(v[i]);    }};/** * Your NestedIterator object will be instantiated and called as such: * NestedIterator i(nestedList); * while (i.hasNext()) cout << i.next(); */