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

[1,2,2,3,4,4,3]

is symmetric:

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

But the following

[1,2,2,null,3,null,3]

is not:

1
/ \
2   2
\   \
3    3

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

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