一、单链表逆序的方法

/*单链表逆序的三种方法（递归、直接翻转指针、头插）*/

下文代码中的list_head 结构体为链表节点结构体。

/*递归方法*/
struct list_head *reverse(struct list_head *head)
{
    struct list_head *new_head;

            /*判断异常 || 结束判断*/
    if (!head || !head->next)/*边界条件*/
        return head;

    new_head = reverse(head->next);/*递归部分*/

    head->next->next = head;/*溯回部分*/
    head->next = NULL;/*记得要赋值为NULL，防止链表错乱*/

    return new_head;/*返回新的链表头*/
}

/*直接翻转指针*/
struct list_head *reverse(struct list_head *head)
{
    struct list_head *prev = NULL;
    struct list_head *next;
    
    while (head != NULL) {
        next = head->next;
        head->next = prev;
        prev = head;
        head = next;
    }

    return prev;
}

/*头插法*/
struct list_head *reverse(struct list_head *head)
{
    struct list_head *z, *j;
    
    j = head->next;/*j用来保存下一个要翻转的结点*/
    head->next = NULL;/*这里相当于把链表头与链表的其余部分断开，作为新的链表头*/

    while (j != NULL) {
        z = j;
        j = j->next;
        z->next = head->next;
        head->next = z;
    }

    return head;
}

参考文章：https://blog.csdn.net/v_xchen_v/article/details/53067448