1+ # Given the root of a binary tree, check whether it is a mirror of itself
2+ # (i.e., symmetric around its center).
3+ 4+ 5+ # Example 1:
6+ # Input: root = [1,2,2,3,4,4,3]
7+ # Output: true
8+ 9+ # Example 2:
10+ # Input: root = [1,2,2,null,3,null,3]
11+ # Output: false
12+ 13+ 14+ # Constraints:
15+ # The number of nodes in the tree is in the range [1, 1000].
16+ # -100 <= Node.val <= 100
17+ 18+ 19+ from typing import Optional
20+ # Definition for a binary tree node.
21+ class TreeNode :
22+ def __init__ (self , val = 0 , left = None , right = None ):
23+ self .val = val
24+ self .left = left
25+ self .right = right
26+ class Solution :
27+ def isSymmetric (self , root : Optional [TreeNode ]) -> bool :
28+ def symmetric (root1 , root2 ):
29+ if (not root1 ) and (not root2 ):
30+ return True
31+ if (not root1 ) or (not root2 ):
32+ return False
33+ if root1 .val != root2 .val :
34+ return False
35+ return (symmetric (root1 .left , root2 .right ) and symmetric (root1 .right , root2 .left ))
36+ 37+ return symmetric (root , root )
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