[LeetCode]Subtree of Another Tree

题目描述：

LeetCode 572. Subtree of Another Tree

Given two non-empty binary trees s and t, check whether tree t has exactly the same structure and node values with a subtree of s. A subtree of s is a tree consists of a node in s and all of this node's descendants. The tree s could also be considered as a subtree of itself.

Example 1:
Given tree s:

     3
    / \
   4   5
  / \
 1   2

Given tree t:

   4 
  / \
 1   2

Return true, because t has the same structure and node values with a subtree of s.

Example 2:
Given tree s:

     3
    / \
   4   5
  / \
 1   2
    /
   0

Given tree t:

   4
  / \
 1   2

Return false.

题目大意：

给定两个非空二叉树s和t，判断t是否是s的子树。s的子树是指由s中某节点及该节点的所有子节点构成的二叉树。

特别的，s是其本身的子树。

解题思路：

嵌套遍历二叉树

Python代码：

# 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 isSubtree(self, s, t):
        """
        :type s: TreeNode
        :type t: TreeNode
        :rtype: bool
        """
        if not s or not t: return not s and not t
        if self.check(s, t): return True
        return self.isSubtree(s.left, t) or self.isSubtree(s.right, t)
        
    def check(self, s, t):
        if not s or not t: return not s and not t
        if s.val != t.val: return False
        return self.check(s.left, t.left) and self.check(s.right, t.right)