101 symmetric tree
101. Symmetric Tree
题目:
https://leetcode.com/problems/symmetric-tree/
难度:
Easy
两棵树symmetric， 有几种可能：
- 均为none ，symmetric
- 左孩子，右孩子都不存在，并且值相等， symmetric
- 右子树 和 另一棵树的左子树相等，左子树 和另一颗树的右子树相等 🌲
class Solution(object):
def isSymmetric(self, root):
"""
:type root: TreeNode
:rtype: bool
"""
if not root:
return True
return self.symmetric(root.left, root.right)
def symmetric(self, l1, l2):
if not l1 or not l2:
if not l1 and not l2:
return True
else:
return False
if l1.val == l2.val:
return self.symmetric(l1.left, l2.right) and self.symmetric(l1.right, l2.left)
else:
return False
