判断二叉树是否相等（leetcode-100）

• 递归依据：两棵树相同位置节点的子树也必须相等
• 递归出口：两个节点全是None，相等；只有一个是None，不等；两个都不是None，但节点值不相等，不等。

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

class Solution(object):
    @classmethod
    def isSameTree(self, p, q):
        if p == None and q == None:
            return True
        elif p == None or q == None:
            return False
        elif p.val != q.val:
            return False
        """
        :type p: TreeNode
        :type q: TreeNode
        :rtype: bool
        """
        return (Solution.isSameTree(p.left, q.left) and Solution.isSameTree(p.right, q.right))