C语言 创建双向循环链表

创建双向循环链表的基本步骤如下：

1. 定义结构体，包含数据和指向前一个和后一个节点的指针。

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

2. 创建头节点，指向自己。

struct Node* head = NULL;
head = (struct Node*)malloc(sizeof(struct Node));
head->prev = head;
head->next = head;

3. 插入节点，可以分为在头部插入、在尾部插入和在中间插入三种情况。

在头部插入：

struct Node* newNode = NULL;
newNode = (struct Node*)malloc(sizeof(struct Node));
newNode->data = value;
newNode->prev = head;
newNode->next = head->next;
head->next->prev = newNode;
head->next = newNode;

在尾部插入：

struct Node* newNode = NULL;
newNode = (struct Node*)malloc(sizeof(struct Node));
newNode->data = value;
newNode->prev = head->prev;
newNode->next = head;
head->prev->next = newNode;
head->prev = newNode;

在中间插入：

struct Node* newNode = NULL;
newNode = (struct Node*)malloc(sizeof(struct Node));
newNode->data = value;
newNode->prev = prevNode;
newNode->next = prevNode->next;
prevNode->next->prev = newNode;
prevNode->next = newNode;

4. 删除节点，类似于插入节点，也可以分为删除头节点、删除尾节点和删除中间节点三种情况。

删除头节点：

struct Node* temp = NULL;
temp = head->next;
head->next = temp->next;
temp->next->prev = head;
free(temp);

删除尾节点：

struct Node* temp = NULL;
temp = head->prev;
head->prev = temp->prev;
temp->prev->next = head;
free(temp);

删除中间节点：

struct Node* temp = NULL;
temp = prevNode->next;
prevNode->next = temp->next;
temp->next->prev = prevNode;
free(temp);

完整代码如下：

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

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

int main() {
    struct Node* head = NULL;
    head = (struct Node*)malloc(sizeof(struct Node));
    head->prev = head;
    head->next = head;
    
    // 在头部插入节点
    struct Node* newNode = NULL;
    newNode = (struct Node*)malloc(sizeof(struct Node));
    newNode->data = 10;
    newNode->prev = head;
    newNode->next = head->next;
    head->next->prev = newNode;
    head->next = newNode;
    
    // 在尾部插入节点
    newNode = (struct Node*)malloc(sizeof(struct Node));
    newNode->data = 20;
    newNode->prev = head->prev;
    newNode->next = head;
    head->prev->next = newNode;
    head->prev = newNode;
    
    // 在中间插入节点
    struct Node* prevNode = head->next;
    newNode = (struct Node*)malloc(sizeof(struct Node));
    newNode->data = 30;
    newNode->prev = prevNode;
    newNode->next = prevNode->next;
    prevNode->next->prev = newNode;
    prevNode->next = newNode;
    
    // 遍历链表
    struct Node* temp = head->next;
    while (temp != head) {
        printf("%d ", temp->data);
        temp = temp->next;
    }
    printf("\n");
    
    // 删除头节点
    temp = head->next;
    head->next = temp->next;
    temp->next->prev = head;
    free(temp);
    
    // 删除尾节点
    temp = head->prev;
    head->prev = temp->prev;
    temp->prev->next = head;
    free(temp);
    
    // 删除中间节点
    prevNode = head->next;
    temp = prevNode->next;
    prevNode->next = temp->next;
    temp->next->prev = prevNode;
    free(temp);
    
    // 遍历链表
    temp = head->next;
    while (temp != head) {
        printf("%d ", temp->data);
        temp = temp->next;
    }
    printf("\n");
    
    return 0;
}