SinglyLinkedListNode* removeDuplicates(SinglyLinkedListNode* llist) {
    if (llist == 0) return 0;
    SinglyLinkedListNode* node = llist;
    while (node && node->next) {
        if (node->data == node->next->data) {
            SinglyLinkedListNode* next = node->next;
            node->next = next->next;
            free(next);
        } else {
            node = node->next;
        }
    }
    return llist;
}