leetcode100 Same Tree

"""
Given two binary trees, write a function to check if they are the same or not.
Two binary trees are considered the same if they are structurally identical and the nodes have the same value.
Example 1:
Input:     1         1
          /        / 
         2   3     2   3
        [1,2,3],   [1,2,3]
Output: true
Example 2:
Input:     1         1
          /           
         2             2
        [1,2],     [1,null,2]
Output: false
Example 3:
Input:     1         1
          /        / 
         2   1     1   2
        [1,2,1],   [1,1,2]
Output: false
"""
class TreeNode:
    def __init__(self, x):
        self.val = x
        self.left = None
        self.right = None

class Solution:
    def isSameTree(self, p: TreeNode, q: TreeNode) -> bool:
        if p ==  None and q == None:
            return True
        # bug代码
        # flag = False
        # while p and q:
        #     if p.val == q.val:
        #         self.isSameTree(p.left, q.left)
        #         self.isSameTree(q.right, q.right)
        #         flag = True
        # return flag
        # 递归注意不用while循环，也应当注意return返回值
        if p and q and p.val == q.val:
            return self.isSameTree(p.left, q.left) and self.isSameTree(p.right, q.right)