# LeetCode 938. Range Sum of BST

## Description

https://leetcode.com/problems/range-sum-of-bst/solution/

Given the `root` node of a binary search tree, return the sum of values of all nodes with a value in the range `[low, high]`.

Example 1:

```Input: root = [10,5,15,3,7,null,18], low = 7, high = 15
Output: 32
```

Example 2:

```Input: root = [10,5,15,3,7,13,18,1,null,6], low = 6, high = 10
Output: 23
```

Constraints:

• The number of nodes in the tree is in the range `[1, 2 * 104]`.
• `1 <= Node.val <= 105`
• `1 <= low <= high <= 105`
• All `Node.val` are unique.

## Explanation

Depth first search to add qualified numbers to the global sum.

## Python Solution

``````# 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 rangeSumBST(self, root: TreeNode, low: int, high: int) -> int:
self.result = 0

self.helper(root, low, high)

return self.result

def helper(self, root, low, high):
if not root:
return

if root.val >= low and root.val <= high:
self.result += root.val

self.helper(root.left, low, high)
self.helper(root.right, low, high)

``````
• Time Complexity: O(N)
• Space Complexity: O(N)