938. Range Sum of BST

Given the root node of a binary search tree, return the sum of values of all nodes with value between L and R (inclusive).
The binary search tree is guaranteed to have unique values.

• Example 1:
  Input: root = [10,5,15,3,7,null,18], L = 7, R = 15
  Output: 32

• Example 2:
  Input: root = [10,5,15,3,7,13,18,1,null,6], L = 6, R = 10
  Output: 23

var rangeSumBST = function(root, L, R) {
    let values = [];
    function inorder(node){
       if(node){
          inorder(node.left);
          if (node.val >= L && node.val <= R) values.push(node.val);
          inorder(node.right);
       }
    }
    inorder(root);
    return values.reduce((a, b) => a + b);
};