Increasing Order Search Tree Python Solution

lcpy gen -n 897   # by problem number
lcpy gen -s increasing_order_search_tree   # by problem name

Input: root = [5,3,6,2,4,null,8,1,null,null,null,7,9]
Output: [1,null,2,null,3,null,4,null,5,null,6,null,7,null,8,null,9]

Input: root = [5,1,7]
Output: [1,null,5,null,7]

from leetcode_py import TreeNode


class Solution:
    # Time: O(n) each node is pushed and popped exactly once
    # Space: O(n) for the node list plus the stack of left-spine ancestors
    def increasing_bst(self, root: TreeNode[int] | None) -> TreeNode[int] | None:
        nodes: list[TreeNode[int]] = []
        stack: list[TreeNode[int]] = []
        current = root

        while current or stack:
            while current:
                stack.append(current)
                current = current.left
            current = stack.pop()
            nodes.append(current)
            current = current.right

        for i, node in enumerate(nodes):
            node.left = None
            node.right = nodes[i + 1] if i + 1 < len(nodes) else None

        return nodes[0] if nodes else None