直接循环

图片解释

ListNode* ReverseList1(ListNode *head)
{
    
    if(head == NULL || head->next == NULL)
    {
        return head;
    } 

    ListNode* tail = NULL;
    ListNode* p = head;
    ListNode* s = head ->next;

    while (s != NULL)
    {
        p->next = tail;
        tail = p;
        p = s;
        s = s->next;
    }
    p->next = tail;

    return p;
}

头插法

图片解释

ListNode* ReverseListInsertHead(ListNode *head)
{
    if(head == NULL || head->next == NULL)
    {
        return head;
    } 

    ListNode* p = NULL;
    ListNode* s = head;
    head = NULL;

    while(s != NULL)
    {
        p = s;
        s = s->next;
        p->next = head;
        head= p;
    }
    
    return head;
}

递归法

ListNode* ReverseListRecur(ListNode *head)
{
    if(head == NULL || head->next == NULL)
    {
        return NULL;
    } 

    ListNode* newhead = ReverseListRecur(head->next);
    head->next->next = head;
    head->next = NULL;

    return newhead;
}

END！