Same Tree

Question

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.

Answer

solution：

# 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):
    def isSameTree(self, p, q):
        """
        :type p: TreeNode
        :type q: TreeNode
        :rtype: bool
        """
        if p is None and q is None:
            return True

        if p is not None and q is not None:
            return p.val == q.val and self.isSameTree(p.left, q.left) and self.isSameTree(p.right, q.right)

        return False

Knowledge：

1. 这道题目是遍历树问题——按路径遍历（迭代）的一个变种，还是使用迭代技术。

2. 在思考时间和空间时，关键是注意以下几点，才能抽象出编程中的迭代：要从头开始将每一个结果每一个步骤都写出来；找到过程中循环的部分，将其进行递归化，其中多个if部分，可以写成并集（and）。

1.先写出主外层结构
isSamTress(self,p,q)
if p is None and q is None:
    return True
if p is not None and q is not None:
    if p.val == q.val:
        ========判断其他结点==========
return False

2.将等号位置代码展开
        if p.left is None and q.left is None:
            return True
        if p.left is not None and q.left is not None:
            if p.left.val == q.left.val:
                ========判断其他结点==========

        if p.right is None and q.right is None:
            return True
        if p.right is not None and q.right is not None:
            if p.right.val == q.right.val:
                ========判断其他结点==========

3.发现有规律性，所以将相似的五行代码，用递归函数表示。