判断二叉树是否对称。
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
分析
题意要求判断一颗二叉树是否是镜像，类似这样的题用递归思想来理解是比较直观的，而且代码也可以写得很优雅。
# 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):
def sym_tree(L,R):
if L and R:
return L.val == R.val and sym_tree(L.left, R.right) and sym_tree(L.right, R.left)
else:
return L == R
return sym_tree(root, root)
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