binary-search-tree-iterator.py

from typing import Optional


# 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()
        ret = node.val

        if node.right:
            node = node.right
            while node:
                self.stack.append(node)
                node = node.left
        return ret

    def hasNext(self) -> bool:
        return len(self.stack) > 0

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