solve: lowestCommonAncestorOfABinarySearchTree

Author: yolophg

lowest-common-ancestor-of-a-binary-search-tree/yolophg.py

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+# Time Complexity: O(log N) on average (for balanced BST), worst case O(N) (skewed tree).
+# Space Complexity: O(1) - don't use extra space, just a few variables.
+
+class Solution:
+    def lowestCommonAncestor(self, root: 'TreeNode', p: 'TreeNode', q: 'TreeNode') -> 'TreeNode':
+         # start from the root
+        node = root 
+
+        while node:  
+            if p.val > node.val and q.val > node.val:
+                # both p and q are in the right subtree, so move right
+                node = node.right  
+            elif p.val < node.val and q.val < node.val:
+                # both p and q are in the left subtree, so move left
+                node = node.left  
+            else:
+                # found the split point where one is on the left and the other is on the right
+                # or when we reach p or q directly (since a node can be its own ancestor)
+                return node  
+
+        return None