leetcode341

/**
 * // 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) {
        begins.push(nestedList.begin());
        ends.push(nestedList.end());
    }

    int next() {
        return (begins.top()++)->getInteger();
    }

    bool hasNext() {
        while(begins.size())        
        {            
            if(begins.top() == ends.top())            
            {                
                begins.pop();                
                ends.pop();            
            }            
            else            
            {                
                auto val = begins.top();                
                if(val->isInteger()) 
                    return true;                
                begins.top()++;                
                begins.push(val->getList().begin());                
                ends.push(val->getList().end());            
            }        
        }        
        return false;

    }

private:
    stack<vector<NestedInteger>::iterator> begins, ends;
};

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