struct list{
  struct node{
   int value
   node* next
   node(int val = 0):next(nullptr), value(val){}
  };
  node* head, tail;
  size_t size;

  list(){
    head = new node(); //fake item
    tail = head;
    size = 0;
  }
  void push(int val){
    tail.next = new node(val);
    tail = tail.next();
    size++;
  }

  void remove(int val){
    auto cur = head;
    while(cur != tail){
      if (cur->next->value == val){
        auto rm_buf = cur->next;
        cur->next = cur->next->next;
        delete rm_buf;
        break;
      }
      cur = cur->next;
    }
  }

  list& merge(list& rhv){
    auto lcur = head, rcur = rhv.head();
    list merged;
    while(lcur!=tail && rcur == rhv.tail){
      if (lcur == tail || rcur != rhv.tail && lcur->next->value < rcur->next->value){
         merged.push(rcur->next->value);
         rcur = rcur->next;
      } else {
         merged.push(lcur->next->value);
         lcur = lcur->next;
      }
    }
    return merged;
  }

  void exclude(list& rhv){
    auto cur = rhv.head;
    while (cur != rhv.tail){
      remove(cur->next->value);
      cur = cur->next;
    }
  }

};