Add solution #1373

Author: JoshCrozier

README.md

@@ -1,4 +1,4 @@
-# 1,260 LeetCode solutions in JavaScript
+# 1,261 LeetCode solutions in JavaScript
 
 [https://leetcodejavascript.com](https://leetcodejavascript.com)
 
@@ -1045,6 +1045,7 @@
 1370|[Increasing Decreasing String](./solutions/1370-increasing-decreasing-string.js)|Easy|
 1371|[Find the Longest Substring Containing Vowels in Even Counts](./solutions/1371-find-the-longest-substring-containing-vowels-in-even-counts.js)|Medium|
 1372|[Longest ZigZag Path in a Binary Tree](./solutions/1372-longest-zigzag-path-in-a-binary-tree.js)|Medium|
+1373|[Maximum Sum BST in Binary Tree](./solutions/1373-maximum-sum-bst-in-binary-tree.js)|Hard|
 1374|[Generate a String With Characters That Have Odd Counts](./solutions/1374-generate-a-string-with-characters-that-have-odd-counts.js)|Easy|
 1380|[Lucky Numbers in a Matrix](./solutions/1380-lucky-numbers-in-a-matrix.js)|Easy|
 1389|[Create Target Array in the Given Order](./solutions/1389-create-target-array-in-the-given-order.js)|Easy|

solutions/1373-maximum-sum-bst-in-binary-tree.js

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+/**
+ * 1373. Maximum Sum BST in Binary Tree
+ * https://leetcode.com/problems/maximum-sum-bst-in-binary-tree/
+ * Difficulty: Hard
+ *
+ * Given a binary tree root, return the maximum sum of all keys of any sub-tree which is also a
+ * Binary Search Tree (BST).
+ *
+ * Assume a BST is defined as follows:
+ * - 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 {number}
+ */
+var maxSumBST = function(root) {
+  let result = 0;
+  traverse(root);
+  return result;
+
+  function traverse(node) {
+    if (!node) return { isBST: true, min: Infinity, max: -Infinity, sum: 0 };
+
+    const left = traverse(node.left);
+    const right = traverse(node.right);
+
+    if (left.isBST && right.isBST && node.val > left.max && node.val < right.min) {
+      const currentSum = node.val + left.sum + right.sum;
+      result = Math.max(result, currentSum);
+      return {
+        isBST: true,
+        min: Math.min(node.val, left.min),
+        max: Math.max(node.val, right.max),
+        sum: currentSum
+      };
+    }
+
+    return { isBST: false, min: 0, max: 0, sum: 0 };
+  }
+};