输入两棵二叉树A，B，判断B是不是A的子结构。（ps：我们约定空树不是任意一个树的子结构）

* solution1: recursion
```python3
# -*- coding:utf-8 -*-
# class TreeNode:
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None
class Solution:
    def HasSubtree(self, pRoot1, pRoot2):
        # write code here
        result = False
        if pRoot1 and pRoot2:
            if pRoo1.val == pRoot2.val:
                result = self.isSubtree(pRoot1,pRoot2)
            if not result:
                result = self.HasSubtree(pRoot1.left,pRoot2)
            if not result:
                result = self.HasSubtree(pRoot1.right,pRoot2)
        return result

    def isSubtree(self,root1,root2):
        if not root2:
            return True
        if not root1:
            return False
        if root1.val != root2.val:
            return False
        return self.isSubtree(root1.left,root2.left) and self.isSubtree(root1.right,root2.right)
```