双向循环链表

1.思路
在双向链表的基础上，让末结点的next指向表头结点，表头结点的pre指向末结点。

2.代码

#include<iostream>using namespace std;struct node {    int data;    node* pPre;    node* pNext;};node* creat() {    node* pHead = (node*)malloc(sizeof(node));    pHead->data = 0;    pHead->pNext = pHead;    pHead->pPre = pHead;    return pHead;}bool isempty(node* pHead) {    return pHead->pNext == pHead;}void print(node* pHead) {    if(pHead == NULL) {        cout << "list failed" << endl;        return;    }    if(isempty(pHead)) {        cout << "list empty" << endl;        return;    }    node* cur = pHead->pNext;    while(cur != pHead) {        cout << cur->data << " ";        cur = cur->pNext;    }    cout << endl;}int getlen(node* pHead) {    int res = 0;    node* tmp = pHead->pNext;    while(tmp != pHead) {        res++;        tmp = tmp->pNext;    }    return res;}void insert(node* pHead, int pos, int n) {    if(pos < 0 || pos > getlen(pHead))        return;    node* pNew = (node*)malloc(sizeof(node));    node* tmp = NULL;    while(pos--) {        pHead = pHead->pNext;    }    pNew->data = n;    tmp = pHead->pNext;    pNew->pNext = tmp;    tmp->pPre = pNew;    pHead->pNext = pNew;    pNew->pPre = pHead;}void del(node* pHead, int pos) {//删除操作的形参是结点的位置    if(pos < 0 || pos > getlen(pHead))        return;    while(pos--) {        pHead = pHead->pNext;    }    node* tmp = pHead->pNext->pNext;    free(pHead->pNext);    pHead->pNext = tmp;    tmp->pPre = pHead;}void destroy(node* pHead) {    while(pHead->pNext != pHead) {        node* tmp = pHead->pNext->pNext;        free(pHead->pNext);        pHead->pNext = NULL;        tmp->pPre = pHead;        pHead->pNext = tmp;    }}int main() {    node* p = creat();    insert(p, 0, 1);    insert(p, 1, 9);    insert(p, 1, 5);    insert(p, 1, 7);    insert(p, 1, 3);    print(p);    del(p, 2);    print(p);    del(p, 0);    del(p, 2);    print(p);    del(p, 0);    del(p, 0);    print(p);    cout << getlen(p) << endl;    destroy(p);    free(p);    p = NULL;    print(p);    return 0;}

3.运行结果