for (ptr1 = l1->head, ptr2 = l2->head; NULL != ptr1;
ptr1 = ptr1->next, last = ptr2, ptr2 = ptr2->next) {
if (NULL == ptr2) {
for (ptr1 = l1->head, ptr2 = l2->head; NULL != ptr1;
ptr1 = ptr1->next, last = ptr2, ptr2 = ptr2->next) {
if (NULL == ptr2) {