Solve : Validate Binary Search Tree

Author: printjin-gmailcom

validate-binary-search-tree/printjin-gmailcom.py

@@ -0,0 +1,14 @@
+class Solution:
+    def isValidBST(self, root):
+        prev = None
+        def inorder(node):
+            nonlocal prev
+            if not node:
+                return True
+            if not inorder(node.left):
+                return False
+            if prev is not None and node.val <= prev:
+                return False
+            prev = node.val
+            return inorder(node.right)
+        return inorder(root)