# LeetCode-Alg-938-Range Sum of BST

## LeetCode-Alg-938-Range Sum of BST

Posted by Jae on May 19, 2019

### 1、题目

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 1:

Input: root = [10,5,15,3,7,null,18], L = 7, R = 15
Output: 32
Example 2:

Input: 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.


### 3、实现

public class Solution {

public int rangeSumBST(TreeNode root, int L, int R) {
if (root == null){
return 0;
}

int sum = 0;
if (root.val >= L && root.val <= R){
// 递归计算左子树+右子树和
sum = root.val + rangeSumBST(root.left, L, R) + rangeSumBST(root.right, L, R);
}else if (root.val < L){
// 左子树不可能存在满足区间的节点
sum = rangeSumBST(root.right, L, R);
}else if (root.val > R){
// 右子树上不可能存在满足区间的节点
sum = rangeSumBST(root.left, L, R);
}
return sum;
} }