Update 0236.二叉树的最近公共祖先.md

problems/0236.二叉树的最近公共祖先.md

@@ -274,25 +274,44 @@ class Solution {
 ```
 
 ## Python 
-
+递归法（版本一）
 ```python
 class Solution:
-    """二叉树的最近公共祖先 递归法"""
-
-    def lowestCommonAncestor(self, root: 'TreeNode', p: 'TreeNode', q: 'TreeNode') -> 'TreeNode':
-        if not root or root == p or root == q:
+    def lowestCommonAncestor(self, root, p, q):
+        if root == q or root == p or root is None:
             return root
-        
+
         left = self.lowestCommonAncestor(root.left, p, q)
         right = self.lowestCommonAncestor(root.right, p, q)
-        
-        if left and right:
-            return root
-        if left:
-            return left
-        return right
-```
 
+        if left is not None and right is not None:
+            return root
+
+        if left is None and right is not None:
+            return right
+        elif left is not None and right is None:
+            return left
+        else: 
+            return None
+```
+递归法（版本二）精简
+```python
+class Solution:
+    def lowestCommonAncestor(self, root, p, q):
+        if root == q or root == p or root is None:
+            return root
+
+        left = self.lowestCommonAncestor(root.left, p, q)
+        right = self.lowestCommonAncestor(root.right, p, q)
+
+        if left is not None and right is not None:
+            return root
+
+        if left is None:
+            return right
+        return left
+
+```
 ## Go 
 
 ```Go