Beat 82.69% in Runtime, 98.90% in memory, only use O(1) memory

Author: ngocquanai

98. Validate Binary Search Tree.py

@@ -0,0 +1,46 @@
+# Definition for a binary tree node.
+# class TreeNode:
+#     def __init__(self, val=0, left=None, right=None):
+#         self.val = val
+#         self.left = left
+#         self.right = right
+class Solution:
+    def isValidBST(self, root):
+        return self.valid_root(root)
+
+    def find_min(self, root):
+        if root == None:
+            return
+        while root.left != None:
+            root = root.left
+        return root.val
+
+    def find_max(self, root):
+        if root == None:
+            return
+        while root.right != None:
+            root = root.right
+        return root.val
+
+    def valid_root(self, root):
+        if root.left == None and root.right == None:
+            return True
+        if root.left == None:
+            bool_condition = root.val < self.find_min(root.right) and self.valid_root(
+                root.right
+            )
+            return bool_condition
+
+        if root.right == None:
+            bool_condition = root.val > self.find_max(root.left) and self.valid_root(
+                root.left
+            )
+            return bool_condition
+
+        general_case = (
+            root.val > self.find_max(root.left)
+            and root.val < self.find_min(root.right)
+            and self.valid_root(root.left)
+            and self.valid_root(root.right)
+        )
+        return general_case