main.cpp

#include <iostream>

// This is your 
struct item {
  // link to next item in the list or "head"
  item *next;

  // link to the previous item or "head"
  item *prev;

  // the value in the list
  int value;

  item(int value=0) : value(value) {}
};
    
// The 
class double_linked_list {
public:
  // placeholder for you to replace.
  item *Tail = nullptr;

  // The head item is the first and last in the list.
  // head <-> one <-> two <-> three <-> head
  item head;

  double_linked_list() {
    // at the start, the head points to itself.CONSTRUCTOR
    head.prev = head.next = &head;
  }

  item *insert(int value) {
    item *new_item = new item(value);
    new_item->prev = &head;
    new_item->next = head.next; // fill this in
	head.next->prev = new_item;
    
	if (head.prev == &head)
	{
		head.prev =new_item;
	} 
	// fill this in
		head.next = new_item;
	
		return new_item;
  }

  item *insert_after(item *prev, int value) {
    item *next = prev->next;
    item *new_item = new item(value);
    new_item->prev = prev;
    new_item->next = next; // fill this in
    prev->next = new_item; // fill this in
    next->prev = new_item; // fill this in

	return new_item;
  }

  item *find(int value) {
     // write a loop here to return the first element with this value
	  item *index = head.next;
	  while (index != &head)
	  {
		  if ((index->value) == value)

			  return index;
		  index = index->next;
	  }

	  return nullptr;
  }

  item *get_first() {
     return head.next;
  }

  void remove(item *victim) {
      item *prev = victim->prev;
      item *next = victim->next;
      victim->prev = nullptr; // fill this in
      victim->next = nullptr; // fill this in
      prev->next = next; // fill this in
      next->prev = prev; // fill this in
  }

  void dump(std::ostream &os) {
    for (item *it = head.next; it != &head; it = it->next) {
      os << "item " << it << " has value " << it->value << "\n";
    }
  }
    
  // unit test
  void unit_test() {
    double_linked_list my_list;
    my_list.insert(1);
    my_list.insert(2);
    my_list.insert(3);
    my_list.insert(4);
    my_list.dump(std::cout);
    auto two = my_list.find(2);
    my_list.remove(two);
    my_list.dump(std::cout);
    auto three = my_list.find(3);
    my_list.insert_after(three, 33);
    my_list.dump(std::cout);
  }
};

int main() {
  double_linked_list my_list;
  my_list.unit_test();
}