solve: validate binary search tree

Author: wogha95

validate-binary-search-tree/wogha95.js

@@ -0,0 +1,40 @@
+/**
+ * TC: O(N)
+ * SC: O(N)
+ * N: total count of tree nodes
+ */
+
+/**
+ * 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 {boolean}
+ */
+var isValidBST = function (root) {
+  return isValidBSTWithBoundary(
+    root,
+    Number.MIN_SAFE_INTEGER,
+    Number.MAX_SAFE_INTEGER
+  );
+
+  function isValidBSTWithBoundary(current, min, max) {
+    if (!current) {
+      return true;
+    }
+
+    if (current.val <= min || max <= current.val) {
+      return false;
+    }
+
+    return (
+      isValidBSTWithBoundary(current.left, min, current.val) &&
+      isValidBSTWithBoundary(current.right, current.val, max)
+    );
+  }
+};