对称二叉树101

class :
    def __init__(self, x):
        self.val = x
        self.left = None
        self.right = None

class Solution:
    def helper(self,left,right):
        
        if not left and not right:
            return True
        if not left or not right:
            return False
        # 递归过程
        if left.val == right.val:
            return self.helper(left.left, right.right) and self.helper(left.right, right.left)
        else:
            return False

    def isSymmetric(self, root):
        """
        :type root: TreeNode
        :rtype: bool
        """
        if not root:
            return True
        else:
            return self.helper(root.left, root.right)

# 例子
tree = TreeNode(1)
left_tree = TreeNode(2)
left_tree.left = TreeNode(3)
left_tree.right = TreeNode(4)
right_tree = TreeNode(2)
right_tree.left = TreeNode(4)
right_tree.right = TreeNode(3)
print(Solution().isSymmetric(tree))