341.Flatten Nested List Iterator.cpp

/**
 * // 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 {
    stack<NestedInteger>Stack;
    
public:
    NestedIterator(vector<NestedInteger> &nestedList) 
    {
        for (int i=nestedList.size()-1; i>=0; i--)
            Stack.push(nestedList[i]);
    }

    int next() 
    {
        int result=Stack.top().getInteger();
        Stack.pop();
        return result;
    }

    bool hasNext() 
    {
        while (!Stack.empty() && Stack.top().isInteger()==false)
        {
            vector<NestedInteger>temp = Stack.top().getList();
            Stack.pop();
            for (int i=temp.size()-1; i>=0; i--)
                Stack.push(temp[i]);
        }
        
        if (Stack.empty()) 
            return false;
        else
            return true;
    }
};

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