> For the complete documentation index, see [llms.txt](https://garylai.gitbook.io/algorithm-and-data-structure/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://garylai.gitbook.io/algorithm-and-data-structure/problems/binary-search/binary-search-tree-iterator.md).

# 173. Binary Search Tree Iterator

[173. Binary Search Tree Iterator](https://leetcode.com/problems/binary-search-tree-iterator/)

```python
# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class BSTIterator:

    def __init__(self, root: Optional[TreeNode]):
        def inorder(node):
            res = []
            if not node:
                return []
            res.extend(inorder(node.left))
            res.append(node.val)
            res.extend(inorder(node.right))
            return res
        self.res = deque(inorder(root))

    def next(self) -> int:
        return self.res.popleft()


    def hasNext(self) -> bool:
        return len(self.res)



# Your BSTIterator object will be instantiated and called as such:
# obj = BSTIterator(root)
# param_1 = obj.next()
# param_2 = obj.hasNext()
```