LeetCode 669. Trim a Binary Search Tree

669. Trim a Binary Search Tree

class Solution {
public:
    TreeNode* trimBST(TreeNode* root, int L, int R) {
        if(root == NULL)
            return NULL;
        if(root->val >R) return trimBST(root->left,L,R);
        if(root->val <L) return trimBST(root->right,L,R);

        root->left = trimBST(root->left,L,R);
        root->right = trimBST(root->right,L,R);
        return root;
    }
};