Add solution #333

Author: JoshCrozier

README.md

@@ -321,6 +321,7 @@
 330|[Patching Array](./solutions/0330-patching-array.js)|Hard|
 331|[Verify Preorder Serialization of a Binary Tree](./solutions/0331-verify-preorder-serialization-of-a-binary-tree.js)|Medium|
 332|[Reconstruct Itinerary](./solutions/0332-reconstruct-itinerary.js)|Hard|
+333|[Largest BST Subtree](./solutions/0333-largest-bst-subtree.js)|Medium|
 334|[Increasing Triplet Subsequence](./solutions/0334-increasing-triplet-subsequence.js)|Medium|
 335|[Self Crossing](./solutions/0335-self-crossing.js)|Hard|
 336|[Palindrome Pairs](./solutions/0336-palindrome-pairs.js)|Hard|

solutions/0333-largest-bst-subtree.js

@@ -0,0 +1,52 @@
+/**
+ * 333. Largest BST Subtree
+ * https://leetcode.com/problems/largest-bst-subtree/
+ * Difficulty: Medium
+ *
+ * Given the root of a binary tree, find the largest subtree, which is also a Binary Search
+ * Tree (BST), where the largest means subtree has the largest number of nodes.
+ *
+ * A Binary Search Tree (BST) is a tree in which all the nodes follow the below-mentioned
+ * properties:
+ * - The left subtree values are less than the value of their parent (root) node's value.
+ * - The right subtree values are greater than the value of their parent (root) node's value.
+ *
+ * Note: A subtree must include all of its descendants.
+ */
+
+/**
+ * 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 largestBSTSubtree = function(root) {
+  let maxSize = 0;
+  traverse(root);
+  return maxSize;
+
+  function traverse(node) {
+    if (!node) return { isBST: true, size: 0, min: Infinity, max: -Infinity };
+
+    const left = traverse(node.left);
+    const right = traverse(node.right);
+    if (left.isBST && right.isBST && node.val > left.max && node.val < right.min) {
+      const size = left.size + right.size + 1;
+      maxSize = Math.max(maxSize, size);
+      return {
+        isBST: true,
+        size,
+        min: Math.min(left.min, node.val),
+        max: Math.max(right.max, node.val)
+      };
+    }
+
+    return { isBST: false, size: 0, min: 0, max: 0 };
+  }
+};