Create 333-largest-bst-subtree.js

Author: everthis

333-largest-bst-subtree.js

@@ -0,0 +1,55 @@
+/**
+
+Given a binary tree, find the largest subtree
+which is a Binary Search Tree (BST),
+where largest means subtree with largest number of nodes in it.
+
+Note:
+A subtree must include all of its descendants.
+
+Example:
+
+Input: [10,5,15,1,8,null,7]
+
+   10 
+   / \ 
+  5  15 
+ / \   \ 
+1   8   7
+
+Output: 3
+Explanation: The Largest BST Subtree in this case is the highlighted one.
+             The return value is the subtree's size, which is 3.
+
+*/
+
+/**
+ * Definition for a binary tree node.
+ * function TreeNode(val) {
+ *     this.val = val;
+ *     this.left = this.right = null;
+ * }
+ */
+/**
+ * @param {TreeNode} root
+ * @return {number}
+ */
+const largestBSTSubtree = function(root) {
+  const res = helper(root)
+  return res[2]
+}
+
+function helper(node) {
+  if (!node) return [Number.MAX_VALUE, -Number.MAX_VALUE, 0]
+  const left = helper(node.left)
+  const right = helper(node.right)
+  if (node.val > left[1] && node.val < right[0]) {
+    return [
+      Math.min(node.val, left[0]),
+      Math.max(node.val, right[1]),
+      left[2] + right[2] + 1
+    ]
+  } else {
+    return [-Number.MAX_VALUE, Number.MAX_VALUE, Math.max(left[2], right[2])]
+  }
+}