341. Flatten Nested List Iterator

/**
 * // 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 {
private:
    vector<int> list;
public:
    void flatten(NestedInteger nl){
        if(nl.isInteger())
            list.push_back(nl.getInteger());
        else{
            const vector<NestedInteger> temp=nl.getList();
            int k=temp.size();
            for(int i=0;i<k;++i){
                flatten(temp[i]);
                
            }
        }
    }


    NestedIterator(vector<NestedInteger> &nestedList) {
        for(int i=0;i<nestedList.size();++i)
            flatten(nestedList[i]);
    }

    int next() {
        int val=list[0];
        list.erase(list.begin());
        return val;
    }

    bool hasNext() {
        return list.size()!=0;
    }
};

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