【題目】

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.

判斷給定的二叉樹是否對稱

【思路】

判斷每一層從左到右與從右到左是否相等

【Python實現】

# -*-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