algorithm - 以下の再帰実装の時間計算量を取得する

Question

/* Function to get diameter of a binary tree */
int diameter(struct node * tree)
{
   /* base case where tree is empty */
    if (tree == 0)
     return 0;

  /* get the height of left and right sub-trees */
  int lheight = height(tree->left);
  int rheight = height(tree->right);

  /* get the diameter of left and right sub-trees */
  int ldiameter = diameter(tree->left);
  int rdiameter = diameter(tree->right);


  return max(lheight + rheight + 1, max(ldiameter, rdiameter));
}


int height(struct node* node)
{
   /* base case tree is empty */
   if(node == NULL)
       return 0;

   /* If tree is not empty then height = 1 + max of left
      height and right heights */   
    return 1 + max(height(node->left), height(node->right));
} 

この実装でツリーの直径を見つける時間の複雑さは O(n^2) で、n はツリー内のノードの数です??