Given two binary trees, write a function to check if they are equal or not.

Two binary trees are considered equal if they are structurally identical and the nodes have the same value.

比较两个树是否相同，包括判断结构和节点的值，同样还是用到递归，加上了空节点的判断可以避免访问空指针。

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

class Solution:
    # @param p, a tree node
    # @param q, a tree node
    # @return a boolean
    def isSameTree(self, p, q):
        if p is None and q is None:
            return True
        elif p is None or q is None:
            return False
        else:
            if p.val == q.val:
                if self.isSameTree(q.left,p.left):
                    return self.isSameTree(p.right,q.right)
            return False

【LeetCode】【Python题解】Same Tree