DIAMETER OF THE BINARY TREE(OPTIMIZED APPROACH)

pair<int,int> fast_diameter(Node*root)
{
     pair<int,int>p;
   
   if(root==NULL)
   {
       p.first=p.second=0;
       return p;
   }
   
   pair<int,int>l=fast_diameter(root->left);
   pair<int,int>r=fast_diameter(root->right);
   
   p.second=1+max(l.second,r.second);
   
   p.first=max(l.first,max(r.first,l.second+r.second+1));
   
   
   return p;    
    
    
    
    
}