Solution2.py

# 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 Solution:
    def trimBST(
        self, root: Optional[TreeNode], low: int, high: int
    ) -> Optional[TreeNode]:
        while root and (root.val < low or root.val > high):
            root = root.left if root.val > high else root.right
        if root is None:
            return None
        node = root
        while node.left:
            if node.left.val < low:
                node.left = node.left.right
            else:
                node = node.left
        node = root
        while node.right:
            if node.right.val > high:
                node.right = node.right.left
            else:
                node = node.right
        return root