adding updates

src/my_project/interviews/google_top_exercises/round_1/19_validate_binary_search_tree.py

@@ -0,0 +1,26 @@
+from typing import Optional
+
+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:
+        def validate(node: Optional[TreeNode], min_val: float, max_val: float) -> bool:
+            # Empty tree is valid
+            if not node:
+                return True
+
+            # Check if current node violates BST property
+            if node.val <= min_val or node.val >= max_val:
+                return False
+
+            # Recursively validate left and right subtrees
+            # Left subtree: all values must be < node.val
+            # Right subtree: all values must be > node.val
+            return (validate(node.left, min_val, node.val) and 
+                    validate(node.right, node.val, max_val))
+
+        return validate(root, float('-inf'), float('inf'))