Add solution #1038

Author: JoshCrozier

README.md

@@ -540,6 +540,7 @@
 1023|[Camelcase Matching](./1023-camelcase-matching.js)|Medium|
 1028|[Recover a Tree From Preorder Traversal](./1028-recover-a-tree-from-preorder-traversal.js)|Hard|
 1037|[Valid Boomerang](./1037-valid-boomerang.js)|Easy|
+1038|[Binary Search Tree to Greater Sum Tree](./1038-binary-search-tree-to-greater-sum-tree.js)|Medium|
 1041|[Robot Bounded In Circle](./1041-robot-bounded-in-circle.js)|Medium|
 1047|[Remove All Adjacent Duplicates In String](./1047-remove-all-adjacent-duplicates-in-string.js)|Easy|
 1051|[Height Checker](./1051-height-checker.js)|Easy|

solutions/1038-binary-search-tree-to-greater-sum-tree.js

@@ -0,0 +1,40 @@
+/**
+ * 1038. Binary Search Tree to Greater Sum Tree
+ * https://leetcode.com/problems/binary-search-tree-to-greater-sum-tree/
+ * Difficulty: Medium
+ *
+ * Given the root of a Binary Search Tree (BST), convert it to a Greater Tree such that every
+ * key of the original BST is changed to the original key plus the sum of all keys greater
+ * than the original key in BST.
+ *
+ * As a reminder, a binary search tree is a tree that satisfies these constraints:
+ * - The left subtree of a node contains only nodes with keys less than the node's key.
+ * - The right subtree of a node contains only nodes with keys greater than the node's key.
+ * - Both the left and right subtrees must also be binary search trees.
+ */
+
+/**
+ * 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
+ * @return {TreeNode}
+ */
+var bstToGst = function(root) {
+  let sum = 0;
+  traverse(root);
+  return root;
+
+  function traverse(node) {
+    if (!node) return;
+    traverse(node.right);
+    sum += node.val;
+    node.val = sum;
+    traverse(node.left);
+  }
+};