****(leetcode) 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:

    1   / \  2   2 / \ / \3  4 4  3

But the following is not:

    1   / \  2   2   \   \   3    3

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.

OJ's Binary Tree Serialization:

The serialization of a binary tree follows a level order traversal, where '#' signifies a path terminator where no node exists below.

Here's an example:

   1  / \ 2   3    /   4    \     5

The above binary tree is serialized as "{1,2,3,#,#,4,#,#,5}".

注意：中序遍历是不行的！！！ 应该分析好题目。不要想当然就写。

/** * Definition for binary tree * struct TreeNode { *     int val; *     TreeNode *left; *     TreeNode *right; *     TreeNode(int x) : val(x), left(NULL), right(NULL) {} * }; */class Solution {    bool function(TreeNode *left, TreeNode *right){        if(NULL == left && NULL == right)            return true;        if((NULL == left && NULL != right)||(NULL != left && NULL == right))            return false;        return (left->val==right->val) && function(left->left,right->right) && function(left->right,right->left);    }public:    bool isSymmetric(TreeNode *root) {        if(root==NULL)            return true;        return function(root->left, root->right);    }};