Symmetric Tree-LeetCode

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

struct TreeNode {
	int val;
	TreeNode *left;
	TreeNode *right;
	TreeNode(int x) : val(x), left(NULL), right(NULL) {}
};
bool issame(TreeNode *root1, TreeNode *root2)
{
	if (root1 == NULL && root2 == NULL)
	{
		return true;
	}
	if (root1 == NULL || root2 == NULL || root1->val != root2->val)
	{
		return false;
	}	
	return issame(root1->left, root2->right)&&issame(root1->right, root2->left);

}
bool isSymmetric(TreeNode *root) {

	if (root == NULL)
		return true;
	return issame(root->left, root->right);
}