Operator overloading Polynomials Doubly linked list

[FatimaRizwan]

This is the operator overloading for the polynomials doubly linked list , this code is working fi9 but i m getting repetition like
1x^1 2x^2 when added with 1x^1 3x^6
2x^1 2x^2 3x^6

but i get those terms also which are subtracted already
like i get
1x^1 2x^2 1x^1 3x^6 2x^1 2x^2 3x^6
please kindly help

list operator - (const list& k)
	{
		node* first;
		first = head;
		node* second;
		second = k.head;
		node* result=head;
		list r;
	
		while (first != NULL)
		{
			second=k.head;
			while (second != NULL)
			{
		if (first->exponent == second->exponent )
		{
					
	result->coefficient	=first->coefficient - second->coefficient;
		result->exponent=first->exponent;
		r.insert(result->coefficient,result->exponent);
									
					
				}
			
		else
		{
				
		r.insert(second->coefficient, second->exponent);
		r.insert(first->coefficient, first->exponent);
			
		}
		second=second->next;
				
		}
			
		first=first->next;
		}
		
		return r;
	}