Range Sum of BST - Easy

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:
	int sum = 0;
	int rangeSumBST(TreeNode* root, int L, int R) {
		if(root == NULL){
			return 0;
		}
		if(root->val > L){
			rangeSumBST(root->left, L, R);
		}
		if(root->val < R){
			rangeSumBST(root->right, L, R);
		}
		if(root->val >= L and root->val <= R){
			sum += root->val;
		}
		return sum;
	}
};