leetcode——341——Flatten Nested List Iterator

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 bynext 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 bynext 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) {               flat(nestedList);        listIter = mList.begin();      }    int next() {        int res = *listIter;          ++listIter;          return res;    }    bool hasNext() {        return listIter != mList.end();    }        void flat(vector<NestedInteger>& nL){          for (auto &it : nL) {              if (it.isInteger())                  mList.push_back(it.getInteger());              else                   flat(it.getList());          }      }     private:      list<int>::iterator listIter;      list<int>mList; };/** * Your NestedIterator object will be instantiated and called as such: * NestedIterator i(nestedList); * while (i.hasNext()) cout << i.next(); */