leetcode——101——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.

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