Add solution #938

Author: JoshCrozier

README.md

@@ -747,6 +747,7 @@
 935|[Knight Dialer](./solutions/0935-knight-dialer.js)|Medium|
 936|[Stamping The Sequence](./solutions/0936-stamping-the-sequence.js)|Hard|
 937|[Reorder Data in Log Files](./solutions/0937-reorder-data-in-log-files.js)|Medium|
+938|[Range Sum of BST](./solutions/0938-range-sum-of-bst.js)|Easy|
 966|[Vowel Spellchecker](./solutions/0966-vowel-spellchecker.js)|Medium|
 970|[Powerful Integers](./solutions/0970-powerful-integers.js)|Easy|
 976|[Largest Perimeter Triangle](./solutions/0976-largest-perimeter-triangle.js)|Easy|

solutions/0938-range-sum-of-bst.js

@@ -0,0 +1,34 @@
+/**
+ * 938. Range Sum of BST
+ * https://leetcode.com/problems/range-sum-of-bst/
+ * Difficulty: Easy
+ *
+ * Given the root node of a binary search tree and two integers low and high, return the sum
+ * of values of all nodes with a value in the inclusive range [low, high].
+ */
+
+/**
+ * Definition for a binary tree node.
+ * function TreeNode(val, left, right) {
+ *     this.val = (val===undefined ? 0 : val)
+ *     this.left = (left===undefined ? null : left)
+ *     this.right = (right===undefined ? null : right)
+ * }
+ */
+/**
+ * @param {TreeNode} root
+ * @param {number} low
+ * @param {number} high
+ * @return {number}
+ */
+var rangeSumBST = function(root, low, high) {
+  return traverse(root);
+
+  function traverse(node) {
+    if (!node) return 0;
+    const value = node.val;
+    if (value < low) return traverse(node.right);
+    if (value > high) return traverse(node.left);
+    return value + traverse(node.left) + traverse(node.right);
+  }
+};