Trim A Binary Search Tree

//Given a binary search tree and the lowest and highest boundaries as L and R, trim the
//tree so that all its elements lies in [L, R] (R >= L). You might need to change the root
//of the tree, so the result should return the new root of the trimmed binary search tree.

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class TrimABinarySearchTree {
    public TreeNode trimBST(TreeNode root, int L, int R) {
        if(root == null) {
            return root;
        }
        if(root.val < L) {
            return trimBST(root.right, L, R);
        }
        if(root.val > R) {
            return trimBST(root.left, L, R);
        }
       
        root.left = trimBST(root.left, L, R);
        root.right = trimBST(root.right, L, R);

        return root;
    }
}