0938. Range Sum of BST

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

Description

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

Example 1:

**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.

Example 2:

**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.

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.

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