snode *skiplist_search(skiplist *list, int key) {
    snode *x = list->header;
    int i;
    for (i = list->level; i >= 1; i--) {
        while (x->forward[i]->key < key)
            x = x->forward[i];
    }
    if (x->forward[1]->key == key) {
        return x->forward[1];
    } else {
        return NULL;
    }
    return NULL;
}

snode *skiplist_search(skiplist *list, int key)
{
    snode *x = list->header;
    int i;
    for (i = list->level; i >= 1; i--) {
        while (x->forward[i]->key < key)
            x = x->forward[i];
    }
    if (x->forward[1]->key == key) {
        return x->forward[1];
    } else {
        return NULL;
    }
    return NULL;
}