LeetCode Problem : Symmetric Tree

Problem

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

Code

bool isSymmetric_r(TreeNode *l,TreeNode *r) {
    if(!l && !r)
        return true;
    if(!l || !r)
        return false;
    if(l->val != r->val)
        return false;
    return (isSymmetric_r(l->left,r->right) && 
    isSymmetric_r(l->right,r->left));
}
bool isSymmetric(TreeNode *root) {
    // IMPORTANT: Please reset any member data you declared, as
    // the same Solution instance will be reused for each test case.
    return isSymmetric_r(root,root);
}