Added validateBinarySearchTree solution

Author: nhistory

validate-binary-search-tree/nhistory.js

@@ -0,0 +1,13 @@
+var isValidBST = function (root) {
+  return validate(root, -Infinity, Infinity);
+};
+
+function validate(node, min, max) {
+  if (!node) return true; // An empty tree is a valid BST
+  if (node.val <= min || node.val >= max) return false; // Current node's value must be between min and max
+
+  // Recursively validate the left and right subtree
+  return (
+    validate(node.left, min, node.val) && validate(node.right, node.val, max)
+  );
+}