/**
 * 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) {
        int sum = 0;
        if (root != null) {
            if (R < root.val) {
                sum = rangeSumBST(root.left, L, R);
            } else if (L > root.val) {
                sum = rangeSumBST(root.right, L, R);
            } else {
                sum = rangeSumBST(root.left, L, root.val) + root.val +
                       rangeSumBST(root.right, root.val, R);
            }
        }
        return sum;
    }
}