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/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class BSTIterator {
public:
    stack<TreeNode *> s;
    TreeNode *curr;

    BSTIterator(TreeNode* root) {
        curr = root;
    }

    int next() {
        while(curr){
            s.push(curr);
            curr = curr->left;
        }
        TreeNode *tmp = s.top();
        s.pop();
        curr = tmp->right;
        return tmp->val;
    }

    bool hasNext() {
        return curr || !s.empty();
    }
};

/**
 * Your BSTIterator object will be instantiated and called as such:
 * BSTIterator* obj = new BSTIterator(root);
 * int param_1 = obj->next();
 * bool param_2 = obj->hasNext();
 */