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