leetcode(40)-对称二叉树

给定一个二叉树，检查它是否是镜像对称的。

https://leetcode-cn.com/problems/symmetric-tree/

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution:
    def isSymmetric(self, root: TreeNode) -> bool:
        stack_left = []
        stack_right = []
        if root is None:return True
        stack_left.append(root.left)
        stack_right.append(root.right)
        while len(stack_left)>0 and len(stack_right)>0:
            left_top = stack_left.pop()
            right_top = stack_right.pop()
            if left_top is None or right_top is None:
                if left_top is None and right_top is None:
                    continue
                else:
                    return False
            if left_top.val!=right_top.val:
                return False
            else:
                stack_left.append(left_top.left)
                stack_left.append(left_top.right)
                stack_right.append(right_top.right)
                stack_right.append(right_top.left)
        if len(stack_right)>0 or len(stack_left)>0:
            return False
        return True