用c语言写一个循环双链表插入算法

循环双链表插入算法的C语言实现如下：

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

// 定义双向链表节点结构体
typedef struct Node {
    int data;
    struct Node* prev;
    struct Node* next;
} Node;

// 定义循环双向链表结构体
typedef struct List {
    Node* head;
    Node* tail;
} List;

// 初始化循环双向链表
void initList(List* list) {
    list->head = NULL;
    list->tail = NULL;
}

// 创建新节点
Node* createNode(int data) {
    Node* node = (Node*)malloc(sizeof(Node));
    node->data = data;
    node->prev = NULL;
    node->next = NULL;
    return node;
}

// 在链表尾部插入节点
void insertAtTail(List* list, int data) {
    Node* node = createNode(data);
    if (list->head == NULL) {
        list->head = node;
        list->tail = node;
        node->prev = node;
        node->next = node;
    } else {
        node->prev = list->tail;
        node->next = list->head;
        list->tail->next = node;
        list->head->prev = node;
        list->tail = node;
    }
}

// 在链表中间插入节点
void insertAtMiddle(List* list, int data, int position) {
    Node* node = createNode(data);
    Node* current = list->head;
    int i = 1;
    while (i < position && current != NULL) {
        current = current->next;
        i++;
    }
    if (current == NULL) {
        printf("Invalid position\n");
        return;
    }
    node->prev = current->prev;
    node->next = current;
    current->prev->next = node;
    current->prev = node;
}

// 打印链表
void printList(List* list) {
    Node* current = list->head;
    if (current == NULL) {
        printf("List is empty\n");
        return;
    }
    do {
        printf("%d ", current->data);
        current = current->next;
    } while (current != list->head);
    printf("\n");
}

int main() {
    List list;
    initList(&list);
    insertAtTail(&list, 1);
    insertAtTail(&list, 2);
    insertAtTail(&list, 3);
    insertAtTail(&list, 4);
    insertAtMiddle(&list, 5, 3);
    printList(&list);
    return ;
}

该算法实现了循环双向链表的初始化、在链表尾部插入节点、在链表中间插入节点和打印链表等功能。其中，insertAtMiddle函数实现了在链表中间插入节点的功能，需要传入链表、要插入的数据和插入的位置三个参数。如果插入位置不合法，会输出"Invalid position"。最后，通过调用printList函数打印链表。