1 files changed, 68 insertions, 0 deletions
diff --git a/98/main.py b/98/main.py
new file mode 100755
index 0000000..4cf245e
--- /dev/null
+++ b/98/main.py
@@ -0,0 +1,68 @@
+#!/usr/bin/env python3
+# not mine
+
+from typing import Optional
+
+# 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: Optional[TreeNode]) -> bool:
+        """dog-slow"""
+
+        def isValid(root, node_min, node_max):
+            if root is None:
+                return True
+
+            if node_min is not None and root.val <= node_min:
+                return False
+            if node_max is not None and root.val >= node_max:
+                return False
+
+            return isValid(root.left, node_min, root.val) and isValid(
+                root.right, root.val, node_max
+            )
+
+        return isValid(root, None, None)
+
+
+def main():
+    node11 = TreeNode(2)
+    node12 = TreeNode(1)
+    node13 = TreeNode(3)
+    node11.left = node12
+    node11.right = node13
+
+    node21 = TreeNode(5)
+    node22 = TreeNode(1)
+    node23 = TreeNode(4)
+    node24 = TreeNode(3)
+    node25 = TreeNode(6)
+    node21.left = node22
+    node21.right = node23
+    node23.left = node24
+    node23.right = node25
+
+    node31 = TreeNode(5)
+    node32 = TreeNode(4)
+    node33 = TreeNode(6)
+    node34 = TreeNode(3)
+    node35 = TreeNode(7)
+    node31.left = node32
+    node31.right = node33
+    node33.left = node34
+    node33.right = node35
+
+    solution = Solution()
+    print(solution.isValidBST(node11))
+    print(solution.isValidBST(node21))
+    print(solution.isValidBST(node31))
+
+
+if __name__ == "__main__":
+    main()