0572._Subtree_of_Another_Tree.md

572. Subtree of Another Tree

难度: Easy

刷题内容

原题连接

• https://leetcode.com/problems/subtree-of-another-tree/

内容描述

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.

解题方案

思路 1 - 时间复杂度: O(N^2)- 空间复杂度: O(1)******

beats 67.88%

class Solution(object):
    def isSubtree(self, s, t):
        """
        :type s: TreeNode
        :type t: TreeNode
        :rtype: bool
        """
        def isSameTree(p, q):
            if not p and not q:
                return True
            if (p and not q) or (not p and q):
                return False
            return p.val == q.val and isSameTree(p.left, q.left) and isSameTree(p.right, q.right)

        if not t:
            return True
        if not s and t:
            return False
        if isSameTree(s, t):
            return True
        return self.isSubtree(s.left, t) or self.isSubtree(s.right, t)