leetcode -- Symmetric Tree -- 简单重点

class Solution(object):

def isSymmetric(self, root):
"""
:type root: TreeNode
:rtype: bool
"""

stack1, stack2 = [], []
res1, res2 = [], []
node1, node2 = root, root
while stack1 or stack2 or node1 or node2 :
if node1:
stack1.append(node1)
node1 = node1.left
else:
node1 = stack1.pop()
if node1 == root:
node1 = None
else:
node1 = node1.right

if node2:
stack2.append(node2)
node2 = node2.right
else:
node2 = stack2.pop()
if node2 == root:
node2 = None
else:
node2 = node2.left

if [x.val for x in stack1] != [x.val for x in stack2]:
return False

return True

class Solution(object):

def issym(self, p, q):

if  p  == None and q == None: return True

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

def isSymmetric(self, root):
"""
:type root: TreeNode
:rtype: bool
"""
if root:
return self.issym(root.left, root.right)
return True