[LeetCode]Symmetric Tree

Symmetric Tree

Given a binary tree, check whether it is a mirror of itself (ie, symmetric around its center).

For example, this binary tree is symmetric:

But the following is not:

Note:
Bonus points if you could solve it both recursively and iteratively.

confused what "{1,#,2,3}" means? > read more on how binary tree is serialized on OJ.

DFS。

 1 /**
 2  * Definition for a binary tree node.
 3  * struct TreeNode {
 4  *     int val;
 5  *     TreeNode *left;
 6  *     TreeNode *right;
 7  *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 8  * };
 9  */
10 class Solution {
11 public:
12     bool check(TreeNode* left,TreeNode* right)
13     {
14         if(!left && !right) return true;
15         if(!left || !right) return false;
16         return (left->val==right->val)&&check(left->left,right->right)&&check(left->right,right->left);
17     }
18     bool isSymmetric(TreeNode* root) {
19         if(!root) return true;
20         return check(root->left,root->right);
21     }
22 };