Update 0101.对称二叉树.md

problems/0101.对称二叉树.md

@@ -442,25 +442,31 @@ class Solution:
 层次遍历
 ```python
 class Solution:
-    def isSymmetric(self, root: Optional[TreeNode]) -> bool:
+    def isSymmetric(self, root: TreeNode) -> bool:
         if not root:
             return True
         
-        que = [root]
+        queue = collections.deque([root.left, root.right])
-        while que:
+        
-            this_level_length = len(que)
+        while queue:
-            for i in range(this_level_length // 2):
+            level_size = len(queue)
-                # 要么其中一个是None但另外一个不是
+            
-                if (not que[i] and que[this_level_length - 1 - i]) or (que[i] and not que[this_level_length - 1 - i]):
+            if level_size % 2 != 0:
                 return False
-                # 要么两个都不是None
+            
-                if que[i] and que[i].val != que[this_level_length - 1 - i].val:
+            level_vals = []
+            for i in range(level_size):
+                node = queue.popleft()
+                if node:
+                    level_vals.append(node.val)
+                    queue.append(node.left)
+                    queue.append(node.right)
+                else:
+                    level_vals.append(None)
+                    
+            if level_vals != level_vals[::-1]:
                 return False
-            for i in range(this_level_length):
+            
-                if not que[i]: continue
-                que.append(que[i].left)
-                que.append(que[i].right)
-            que = que[this_level_length:]
         return True
 ```