【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.

class Solution {
public:
bool isSym(TreeNode* n1,TreeNode* n2)
{
if(n1==NULL&&n2!=NULL) return false;
if(n1!=NULL&&n2==NULL) return false;
if(n1==NULL&&n2==NULL) return true;
if(n1->val!=n2->val) return false;

return isSym(n1->left,n2->right)&&isSym(n1->right,n2->left);
}

bool isSymmetric(TreeNode* root) {
if(root==NULL||(!root->left&&!root->right)) return true;
return isSym(root->left,root->right);
}
};