[prograsshopper] week 02 Solutions

validate-binary-search-tree/prograsshopper.py

@@ -0,0 +1,22 @@
+# 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:
+        # Time Complexity: O(N)
+        # Space Complexity: O(N)
+        def check_valid(node, min_val, max_val):
+            if not node:
+                return True
+            if not (min_val < node.val < max_val):
+                return False
+            return (
+                    check_valid(node.left, min_val, node.val)
+                    and
+                    check_valid(node.right, node.val, max_val)
+            )
+
+        return check_valid(root, float('-inf'), float('inf'))