101. Symmetric Tree
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
Note: Bonus points if you could solve it both recursively and iteratively.
Solution:
# 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 not root:
return True
else:
return self.mirror(root.left, root.right)
def mirror(self, left, right):
if not left or not right:
return left == right
if left.val != right.val:
return False
return self.mirror(left.left, right.right) and self.mirror(left.right, right.left)
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