剑指offer28.对称的二叉树

判断二叉树是不是对称的

思路：递归过程

• 判断当前指针两个节点值是否相等
• 判断A的右子树和B的左子树是否对称
• 判断A的左子树和B的右子树是否对称

class Solution(object):
    def isSymmetric(self, root):
        """
        :type root: TreeNode
        :rtype: bool
        """
        return self.is_symmetrical_core(root, root)

    def is_symmetrical_core(self,node1, node2):
        if node1 is None and node2 is None:
            return True
        if node1 is None or node2 is None:
            return False
        if node1.val != node2.val:
            return False
    
        return self.is_symmetrical_core(node1.left, node2.right) and     self.is_symmetrical_core(node1.right, node2.left)