单选题库

ListNode* reverseLinkedList(ListNode* head) {
    ListNode* prev = nullptr;
    ListNode* current = head;
    while (current != nullptr) {
        ListNode* next = current->next;
        current->next = next;
        prev = current;
        current = next;
    }
    return prev;
}

int gcd(int a, int b) {
    while (b != 0) {
        ________________________
    }
    return a;
}