Range Sum of BST Python Solution with Tests

lcpy gen -n 938   # by problem number
lcpy gen -s range_sum_of_bst   # by problem name

Input: root = [10,5,15,3,7,null,18], low = 7, high = 15
Output: 32
Explanation: Nodes 7, 10, and 15 are in the range [7, 15]. 7 + 10 + 15 = 32.

Input: root = [10,5,15,3,7,13,18,1,null,6], low = 6, high = 10
Output: 23
Explanation: Nodes 6, 7, and 10 are in the range [6, 10]. 6 + 7 + 10 = 23.

from leetcode_py import TreeNode


class Solution:
    # Time: O(n)
    # Space: O(h) where h is the tree height
    def range_sum_bst(self, root: TreeNode[int] | None, low: int, high: int) -> int:
        if root is None:
            return 0
        if root.val < low:
            # Entire left subtree is below the range
            return self.range_sum_bst(root.right, low, high)
        if root.val > high:
            # Entire right subtree is above the range
            return self.range_sum_bst(root.left, low, high)
        return (
            root.val
            + self.range_sum_bst(root.left, low, high)
            + self.range_sum_bst(root.right, low, high)
        )