这还不够简洁？

struct ListNode *plusAB( struct ListNode *a, struct ListNode *b ) {
    struct ListNode node = {-1,NULL}, *tail = NULL;
    int jw = 0;

    tail = &node;
    while( a != NULL || b != NULL || jw != 0 ) {
        jw += a != NULL ? a->val : 0;
        jw += b != NULL ? b->val : 0;
        a = a != NULL ? a->next : a;
        b = b != NULL ? b->next : b;
        tail->next = (struct ListNode *) malloc( sizeof(*tail) );
        tail->next->val = jw % 10; // 取余数.
        tail->next->next = NULL;
        tail = tail->next;
        jw = jw / 10; // 取商.
    }

    return node.next;
}