Write code to remove duplicates from an unsorted linked list. FOLLOW UP How would you solve this problem if a temporary buffer is not allowed?

CareerCup2.1.cpp

#include <iostream>
#include <hash_set>
#include <string>

class Node
{
  public:
	int data;
	Node* next;
};

void Input(Node*, Node*);
void Output(Node*, Node*);
void DelDuplication1(Node*, Node*);
void DelDuplication2(Node*, Node*);
void Del(Node*, Node*);
int main()
{
	Node *head = new Node();
	Node *end = new Node();
	Input(head,end);
	DelDuplication2(head,end);
	Output(head,end);
	Del(head,end);
	return 0;
}
void DelDuplication1(Node* head, Node* end)
{
	using namespace __gnu_cxx;
	hash_set<int> hashset;
	Node *current = head;
	while(current->next!=end)
	{
		Node *former = current;
		current = current->next;
		if(hashset.find(current->data)==hashset.end())
		{
			hashset.insert(current->data);
		}
		else
		{
			former->next = current->next;
			delete current;
			current = former;
		}
	}
}
void DelDuplication2(Node* head, Node* end)
{
	Node *current = head;
	while(current->next!=end)
	{
		current = current->next;
		Node *iter = current;
		while(iter->next!=end)
		{
			Node *former = iter;
			iter = iter->next;
			if(iter->data==current->data)
			{
				former->next = iter->next;
				delete iter;
				iter = former;
			}
		}
	}
}
//input the linked list
void Input(Node* head, Node* end)
{
	using namespace std;
	int num;
	Node *current = head;
	while(cin>>num)
	{
		current->next = new Node();
		current = current->next;
		current->data = num;
	}
	current->next = end;
}
void Output(Node* head, Node* end)
{
	using namespace std;
	Node *current = head;
	while(current->next!=end)
	{
		current = current->next;
		cout<<current->data<<" ";
	}
	cout<<endl;
}
void Del(Node* head, Node* end)
{
	Node *current = head;
	while(current->next!=end)
	{
		Node* former = current;
		current = current->next;
		former->next = current->next;
		delete current;
		current = former;
	}

}