/**
 * // 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) {
        nested_int_stack_.push(&nestedList);
        nested_int_pos_stack_.push(0);
        MoveTillNextInteger();
    }

    int next() {
        MoveTillNextInteger();
        return nested_int_stack_.top()->at(nested_int_pos_stack_.top()).getInteger();
    }

    bool hasNext() {
        MoveTillNextInteger();
        return !nested_int_stack_.empty();
    }

private:
    stack<vector<NestedInteger>*> nested_int_stack_;
    stack<int> nested_int_pos_stack_;

    void MoveTillNextInteger() {
        int curr_pos = nested_int_pos_stack_.top();

        while (!nested_int_stack_.empty() && (curr_pos == nested_int_stack_.top()->size() ||
               !nested_int_stack_.top()->at(curr_pos).isInteger())) {

            nested_int_pos_stack_.pop();

            if (curr_pos == nested_int_stack_.top()->size()) {
                nested_int_stack_.pop();
                curr_pos = nested_int_pos_stack_.top();
                continue;
            }

            nested_int_pos_stack_.push(curr_pos + 1);
            nested_int_stack_.push(&nested_int_stack_.top()->at(curr_pos).getList());
            nested_int_pos_stack_.push(0);
            curr_pos = 0;
        }
    }
};

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