Check whether two trees are structurally identical

/*
 Given two trees, return true if they are
 structurally identical.
*/
int sameTree(struct node* a, struct node* b) {
  // 1. both empty -> true
  if (a==NULL && b==NULL) return(true);
  // 2. both non-empty -> compare them
  else if (a!=NULL && b!=NULL) {
    return(
      a->data == b->data &&
      sameTree(a->left, b->left) &&
      sameTree(a->right, b->right)
    );
  }
  // 3. one empty, one not -> false
  else return(false);
}