用C语言编写算法逆置一个带头结点的双链表。

下面是C语言代码实现双向链表逆置的算法：

#include <stdio.h>
#include <stdlib.h>

struct Node {
    int data;
    struct Node* next;
    struct Node* prev;
};

void insertAtEnd(struct Node** head_ref, int new_data)
{
    struct Node* new_node = (struct Node*)malloc(sizeof(struct Node));
    struct Node* last = *head_ref;
    new_node->data = new_data;
    new_node->next = NULL;
    if (*head_ref == NULL) {
        new_node->prev = NULL;
        *head_ref = new_node;
        return;
    }
    while (last->next != NULL)
        last = last->next;
    last->next = new_node;
    new_node->prev = last;
    return;
}

void printList(struct Node* node)
{
    struct Node* last;
    printf("\nTraversal in forward direction \n");
    while (node != NULL) {
        printf(" %d ", node->data);
        last = node;
        node = node->next;
    }

    printf("\nTraversal in reverse direction \n");
    while (last != NULL) {
        printf(" %d ", last->data);
        last = last->prev;
    }
}

void reverse(struct Node** head_ref)
{
    struct Node* current = *head_ref;
    struct Node* temp = NULL;
    while (current != NULL) {
        temp = current->prev;
        current->prev = current->next;
        current->next = temp;
        current = current->prev;
    }
    if (temp != NULL)
        *head_ref = temp->prev;
}

int main()
{
    struct Node* head = NULL;
    insertAtEnd(&head, 1);
    insertAtEnd(&head, 2);
    insertAtEnd(&head, 3);
    insertAtEnd(&head, 4);
    insertAtEnd(&head, 5);

    printf("Original doubly linked list is: ");
    printList(head);

    reverse(&head);

    printf("\nReversed doubly linked list is: ");
    printList(head);

    return 0;
}

这段代码定义了一个双向链表的结构体 `Node`，并提供了向链表尾部插入节点的函数 `insertAtEnd`，遍历链表的函数 `printList`，以及逆置链表的函数 `reverse`。

在 `main` 函数中，我们创建了一个带头结点的双向链表，并调用 `printList` 函数打印出原始链表的内容。然后我们调用 `reverse` 函数逆置链表，并再次调用 `printList` 函数打印出逆置后的链表的内容。

逆置链表的实现方法是从头结点开始，依次交换前驱和后继指针，直到链表末尾。最后再把头结点指向链表末尾，完成逆置。