Read the How to prepare for an interview series at my blog: http://se7so.blogspot.com/2014/01/how-to-prepare-for-interview.html

prob10.cpp

node* sum(node* num1, node* num2) {
	
	node* l1 = num1, *l2 = num2;
	
	node* res = new node(0);
	
	int rem = 0;
	while(l1 && l2) {
		int num = l1->d+l2->d+rem;
		
		if(num >= 10) {
			insert(res, num-10);
			rem = num/10;
		}
		else {
			rem = 0;
			insert(res, num);
		}
		
		l1 = l1->nxt;
		l2 = l2->nxt;
	}

	node* tmp = l1 ? l1 : l2;
	
	while(tmp) {
		int num = tmp->d+rem;
		insert(res, num-10);
		rem = num/10;
		tmp = tmp->nxt;
	}
	
	if(rem)
		insert(res, rem);
		
	tmp = res;
	res = res->nxt;
	delete tmp;
	
	return res;
}