Leetcode - 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:

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 isEqual(root->left, root->right);
}
bool isEqual(TreeNode *lhs, TreeNode *rhs)
{
if(!rhs&&!lhs)
return true;
if((lhs&&!rhs)||(!lhs&&rhs))
return false;
return (lhs->val==rhs->val)&&isEqual(lhs->left,rhs->right)&&isEqual(lhs->right,rhs->left);
}
};