1、思路

模板题，记下来就好。

2、代码

//反转单链表
list_node * reverse_list(list_node * head)
{
    if (head == nullptr || head->next == nullptr) return head;

    list_node *pre = nullptr, *next = nullptr;
    while (head != nullptr)
    {
        next = head->next;
        head->next = pre;
        pre = head;
        head = next;
    }

    return pre;
}

//反转双链表
double_list_node * reverse_double_list(double_list_node * head)
{
    if (head == nullptr || head->next == nullptr) return head;

    double_list_node *pre = nullptr, *next = nullptr;
    while (head != nullptr)
    {
        next = head->next;
        head->next = pre;
        head->pre = next;   //与反转单链表不同的就是多了这一行
        pre = head;
        head = next;
    }

    return pre;
}