LeetCode 572 Subtree of Another Tree

题目：

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 scould 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.

题目链接

题意：

给两个非空的二叉树s和t，编写函数实现判断t是否为s的子树。其中，s也可以是它自己的子树。

先序遍历二叉树s，当判断s当前结点的val和t的val相同，则进入判断子树的函数，同步遍历s和t，看是否完全相同，假如不相同，则进行下一层遍历。

代码如下：

class Solution {public:    bool dfsSubtree(TreeNode* s, TreeNode * t) {  // 判断两个子树是否完全相同        if ((!s && t) || (s && !t)) return false;        else if (!s && !t) return true;        return s->val == t->val && dfsSubtree(s->left, t->left) && dfsSubtree(s->right, t->right);    }    bool isSubtree(TreeNode* s, TreeNode* t) {        if ((!s && t) || (s && !t)) return false;        return ((s->val == t->val) && dfsSubtree(s, t) || isSubtree(s->left, t) || isSubtree(s->right, t)); // 先序遍历同时判断s->val和t->val    }};