原题
给定一个二叉树，检查他是不是自己的镜像(轴对称)
样例
1
/ \
2 2
/ \ / \
3 4 4 3
是对称二叉树
1
/ \
2 2
\ \
3 3
不是对称二叉树
解题思路
- 写一个helper函数，递归求解，但注意helper函数的形参left和right不是指的左儿子和右儿子。那上面的例子为例，我们要传入3，3和4，4
- Divide and Conquer的思路 - 如果
left.left, right.right和left.right, right.left都对称则整棵树对称
完整代码
# Definition for a binary tree node.
# class TreeNode(object):
# def __init__(self, x):
# self.val = x
# self.left = None
# self.right = None
class Solution(object):
def isSymmetric(self, root):
"""
:type root: TreeNode
:rtype: bool
"""
if root:
return self.helper(root.left, root.right)
return True
def helper(self, left, right):
if left is None and right is None:
return True
if left and right and left.val == right.val:
return self.helper(left.left, right.right) and \
self.helper(left.right, right.left)
return False
