1 '''
2 给定一个二叉树，检查它是否是镜像对称的。
3 '''
4
5
6 class TreeNode:
7 def __init__(self, x):
8 self.val = x
9 self.left = None
10 self.right = None
11
12
13 class Solution:
14 def isSymmetric(self, root):
15 """
16 :type root: TreeNode
17 :rtype: bool
18 """
19 if not root:
20 return True
21 else:
22 # p=root.left;q=root.right
23 def isSameTree(p, q):
24 if not p and not q: # 两二叉树皆为空，递归边界，两者皆为空返回真
25 return True
26 if p and q and p.val == q.val:
27 l = isSameTree(p.left, q.right)
28 r = isSameTree(p.right, q.left)
29 return l and r # 需要l与r皆为true时，才返回真。只用最后一次递归边界return值
30 else:
31 return False
32
33 return isSameTree(root.left, root.right)
34
35
36 if __name__ == '__main__':
37 n = [1, 2, 2, 3, 4, 4, 3]
38 root = TreeNode(1)
39 l1 = root.left = TreeNode(2)
40 r1 = root.right = TreeNode(2)
41 l2ll = l1.left = TreeNode(3)
42 l2lr = l1.right = TreeNode(4)
43 l2rl = r1.left = TreeNode(4)
44 l2rr = r1.right = TreeNode(3)
45 ret = Solution().isSymmetric(root)
46 print(ret)
