6/22/2017 - 4:23 AM

## 101. Symmetric Tree

1. Symmetric Tree
``````# 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 == None:
return True
return self.check(root.left, root.right)
def check(self, node1, node2):
if node1 == None and node2 == None:
return True
elif node1 == None or node2 == None:
return False
else:
cond1 = node1.val == node2.val
cond2 = self.check(node1.right, node2.left)
cond3 = self.check(node1.left, node2.right)
return cond1 and cond2 and cond3``````

https://leetcode.com/problems/symmetric-tree/#/description

Given a binary tree, check whether it is a mirror of itself (ie, symmetric around its center).

For example, this binary tree `[1,2,2,3,4,4,3]` is symmetric:

``````    1
/ \
2   2
/ \ / \
3  4 4  3
``````

But the following `[1,2,2,null,3,null,3]` is not:

``````    1
/ \
2   2
\   \
3    3
``````