LeetCode 101 Symmertic Tree(Python详解及实现)

【题目】

Given a binary tree, check whether it is amirror 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  44  3

But the following [1,2,2,null,3,null,3] isnot:

    1

   /\

 2   2

  \   \

  3    3

Note:

Bonus points if you could solve it bothrecursively and iteratively.

判断给定的二叉树是否对称

 

【思路】

判断每一层从左到右与从右到左是否相等

 

 

【Python实现】

# -*-coding: utf-8 -*-
"""
Createdon Fri Aug 11 17:06:34 2017

@author:Administrator
"""

#Definition for a binary tree node.
classTreeNode(object):
def __init__(self, x):
self.val = x
self.left = None
self.right = None

classSolution(object):
def isSymmetric(self, root):
"""
:type root: TreeNode
:rtype: bool
"""
if root:
return self.symmetriTree(root.left,root.right)
return True
def symmetriTree(self, p, q):
if p is None and q is None:
return True

if p and q and p.val == q.val:
return self.symmetriTree(p.left,q.right) and self.symmetriTree(p.right, q.left)
return False

if __name__== '__main__':
S = Solution()
l1 = TreeNode(4)
l2 = TreeNode(2)
l3 = TreeNode(6)
l4 = TreeNode(1)
l5 = TreeNode(5)
l6 = TreeNode(3)
l7 = TreeNode(7)

root = l1

l1.left = l2
l1.right = l3

l2.left = l4
l2.right = l5
l3.left = l6
l3.right = l7