Add solution #538

Author: JoshCrozier

README.md

@@ -428,6 +428,7 @@
 530|[Minimum Absolute Difference in BST](./0530-minimum-absolute-difference-in-bst.js)|Easy|
 532|[K-diff Pairs in an Array](./0532-k-diff-pairs-in-an-array.js)|Medium|
 537|[Complex Number Multiplication](./0537-complex-number-multiplication.js)|Medium|
+538|[Convert BST to Greater Tree](./0538-convert-bst-to-greater-tree.js)|Medium|
 541|[Reverse String II](./0541-reverse-string-ii.js)|Easy|
 542|[01 Matrix](./0542-01-matrix.js)|Medium|
 543|[Diameter of Binary Tree](./0543-diameter-of-binary-tree.js)|Easy|

solutions/0538-convert-bst-to-greater-tree.js

@@ -0,0 +1,40 @@
+/**
+ * 538. Convert BST to Greater Tree
+ * https://leetcode.com/problems/convert-bst-to-greater-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 convertBST = 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);
+  }
+};