2023-09-12 11:01:45 +0000 UTC

# 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]):
        self._stack = []
        while root:
            self._stack.append(root)
            root = root.left

    def next(self) -> int:
        node = self._stack.pop()
        right = node.right
        while right:
            self._stack.append(right)
            right = right.left
        
        return node.val

    def hasNext(self) -> bool:
        return self._stack


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