class BSTIterator {
     stack<TreeNode*>st;
public:

    BSTIterator(TreeNode* root) {

        mypush(root);

    }

    /** @return whether we have a next smallest number */
    bool hasNext() {

        return !st.empty();

    }


    /** @return the next smallest number */
    int next() {

       TreeNode *temp = st.top();
        st.pop();
        mypush(temp->right);
        return temp->val;


    }

   void mypush(TreeNode* node)
    {
        while(node!=NULL)
        {
            st.push(node);
            node=node->left;
        }
    }
};