Add level order traversal

problems/0101.对称二叉树.md

@@ -437,6 +437,41 @@ class Solution:
         return True
 ```
 
+层序遍历
+
+```python
+class Solution:
+    def isSymmetric(self, root: TreeNode) -> bool:
+        if not root: return True
+        que, cnt = [[root.left, root.right]], 1
+        while que:
+            nodes, tmp, sign = que.pop(), [], False
+            for node in nodes:
+                if not node:
+                    tmp.append(None)
+                    tmp.append(None)
+                else:
+                    if node.left:
+                        tmp.append(node.left)
+                        sign = True
+                    else:
+                        tmp.append(None)
+                    if node.right:
+                        tmp.append(node.right)
+                        sign = True
+                    else:
+                        tmp.append(None)
+            p1, p2 = 0, len(nodes) - 1
+            while p1 < p2:
+                if (not nodes[p1] and nodes[p2]) or (nodes[p1] and not nodes[p2]): return False
+                elif nodes[p1] and nodes[p2] and nodes[p1].val != nodes[p2].val: return False
+                p1 += 1
+                p2 -= 1
+            if sign: que.append(tmp)
+            cnt += 1
+        return True
+```
+
 ## Go
 
 ```go