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.

/**

 * Definition for binary tree

 * struct TreeNode {

 *     int val;

 *     TreeNode *left;

 *     TreeNode *right;

 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}

 * };

 */

class Solution {

public:

    bool isSymmetric(TreeNode *root) 

    {

        if(root==NULL)

            return true;

        return isMirror(root->left,root->right);

    }

    bool isMirror(TreeNode* left,TreeNode* right)

    {

        if(left==NULL && right==NULL)

            return true;

        if(left==NULL || right==NULL)

            return false;

        if(left->val!=right->val)

            return false;

        return isMirror(left->left,right->right) && isMirror(left->right,right->left);

    }

};