Lowest Common Ancestor of a Binary Search Tree

python/leetcode/Lowest Common Ancestor of a Binary Search Tree.py

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+from python.leetcode.libs.tree import TreeNode
+
+
+class Solution:
+    def lowestCommonAncestor(self, root: 'TreeNode', p: 'TreeNode', q: 'TreeNode') -> 'TreeNode':
+
+        min_node, max_node = (p, q) if p.val < q.val else (q, p)
+
+        answer = None
+
+        def traceback(node):
+            nonlocal answer
+            if not node:
+                return
+
+            if node.val >= min_node.val and node.val <= max_node.val:
+                answer = node
+                return
+
+            if node.val < min_node.val and node.val < max_node.val:
+                traceback(node.right)
+            else:
+                traceback(node.left)
+
+        traceback(root)
+
+        return answer
+
+
+if __name__ == "__main__":
+    obj = Solution()
+
+    root = TreeNode.array_to_tree([6, 2, 8, 0, 4, 7, 9, None, None, 3, 5])
+    p = 2
+    q = 4
+    assert obj.lowestCommonAncestor(root, root.left, root.left.right).val == root.left.val
+
+    root = TreeNode.array_to_tree([6, 2, 8, 0, 4, 7, 9, None, None, 3, 5])
+    assert obj.lowestCommonAncestor(root, root.left, root.right).val == root.val