Description
Given the root node of a binary search tree, return the sum of values of all nodes with value between L and R (inclusive).
The binary search tree is guaranteed to have unique values.
Example
Example 1:1
2Input: root = [10,5,15,3,7,null,18], L = 7, R = 15
Output: 32
Example 2:1
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27Input: root = [10,5,15,3,7,13,18,1,null,6], L = 6, R = 10
Output: 23
**Note:**
The number of nodes in the tree is at most 10000.
The final answer is guaranteed to be less than 2^31.
## Solution
```java
/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
class Solution {
public int rangeSumBST(TreeNode root, int L, int R) {
if (root == null) return 0;
if (root.val < L) return rangeSumBST(root.right, L, R);
if (root.val > R) return rangeSumBST(root.left, L, R);
return root.val + rangeSumBST(root.left, L, R) + rangeSumBST(root.right, L, R);
}
}