938. Range Sum of BST

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

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);
        } else if (root.val > R) {
            return rangeSumBST(root.left, L, R);
        } else {
            return root.val + rangeSumBST(root.left, L, root.val) + 
            rangeSumBST(root.right, root.val, R);
        }
    }
}