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