Binary Search Tree Iterator

main.py

class BSTIterator:
    def __init__(self, root: TreeNode):
        self.stack = []
        self.curr_node = root

    def next(self) -> int:
        while self.curr_node:
            self.stack.append(self.curr_node)
            self.curr_node = self.curr_node.left
        self.curr_node = self.stack.pop()
        ans = self.curr_node.val
        self.curr_node = self.curr_node.right
        return ans

    def hasNext(self) -> bool:
        return len(self.stack) != 0 or self.curr_node is not None