输入两棵二叉树A和B，判断B是不是A的子结构。

输入：A = [1,2,3], B = [3,1]
输出：false

输入：A = [3,4,5,1,2], B = [4,1]
输出：true

思路：对称性递归

https://leetcode-cn.com/problems/shu-de-zi-jie-gou-lcof/solution/yi-pian-wen-zhang-dai-ni-chi-tou-dui-che-uhgs/