[WHYjun] WEEK 02 solutions - (5/5)

Author: WHYjun

validate-binary-search-tree/WHYjun.py

@@ -0,0 +1,17 @@
+# 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:
+        # https://stackoverflow.com/a/37300370
+        return self.isValid(root, float('-inf'), float('inf'))
+
+    def isValid(self, node: Optional[TreeNode], low: float, high: float):
+        if node is None:
+            return True
+        if node.val <= low or node.val >= high:
+            return False
+        return self.isValid(node.left, low, node.val) and self.isValid(node.right, node.val, high)