双向循环链表

双向循环链表：
1.首先，双向链表通常采用带表头结点的循环链表形式，即双向循环链表。双向循环链表在双向链表的基础上，将表头结点的前驱指针指向尾结点，尾结点的后驱指针指向头结点，首尾相连形成一个双向环。双向循环链表可方便地获取当前结点的前驱结点，不必像单向循环链表那样从头开始遍历；而其循环的特性又可方便地从任一结点出发单向遍历整个链表，不必像双向链表那样根据方向而使用不同的指针域。

2.如图所示：

3.代码如下：

#include"stdio.h"#include"stdlib.h"#include"assert.h"#pragma warning (disable:4996)typedef int DataType;typedef struct DCLNode{    struct DCLNode* _pNext;    struct DCLNode* _pPre;    DataType _data;}Node, *PNode;//初始化双向循环列表void DCLInit(PNode* ppHead){    assert(ppHead);    *ppHead = (PNode)malloc(sizeof(Node));    if (NULL == *ppHead)        assert(0);    (*ppHead)->_pNext = *ppHead;    (*ppHead)->_pPre = *ppHead;}//构造一个新结点PNode DCLBuyNode(DataType data){    PNode pNewNode = (PNode)malloc(sizeof(Node));    if (NULL == PNewNode)        assert(0);    pNewNode->_data = data;    pNewNode->_pNext = NULL;    pNewNode->_pPre = NULL;    return pNewNode;}//尾插void DCLPushBack(PNode pHead, DataType data){    PNode DCLBuyNode(data);    PNode pTailNode = NULL;    assert(pHead);    pTailNode = pHead->_pPre;    pTailNode->_pNext = pNewNode;    pNewNode->_pPre = pTailNode;    pNewNode->_pNext = pHead;    pHead->_pPre = pTailNode;}//尾删void DCLPopBack(PNode pHead){    if (pHead->_pNext == pHead)    {        return;    }    else    {        PNode pPreTail = pHead->_pPre->_pPre;        free(pPreTail->_pNext);        pPreTail->_pNext = pHead;        pHead->_pPre = pPreTail;    }}//头插void DCLPushFront(PNode pHead, DataType data){    PNode pNewNode = DCLBuyNode(data);    assert(pHead);    pNewNode->_pNext = pHead->_pNext;    pHead->_pNext->_pPre = pNewNode;    pNewNode->_pPre = pHead;    pHead->_pNext = pNewNode;}//头删void DCLPopFront(PNode pHead){    if (pHead->_pNext == pHead)    {        return;    }    else    {        PNode pDel = pHead->_pNext;        pHead->_pNext = pDel->_pNext;        pDel->_pNext->_pPre = pHead;        free(pDel);    }}//打印void DCLPrintList(PNode pHead){    pNode pCur = NULL;    assert(pHead);    pCur = pHead->_pNext;    while (pCur != pHead)    {        printf("%d->",pCur->_data);    }    printf("\n");}//任意位置删除void DCLInsert(PNode pos, DataType data){    PNode pNewNode = DCLBuyNode(data);    assert(pNewNode);    pNewNode->_pNext = pos;    pos->_pPre->_pNext = pNewNode;    pNewNode->_pPre = pos->_pPre;    pos->_pPre = pNewNode;}//任意位置删除void DCLErase(PNode pos){    pos->_pPre->_pNext = pos->_pNext;    pos->_pNext->_pPre = pos->_pPre;    free(pos);}//查找元素PNode DCLFind(PNode pHead, DataType data){    PNode pCur = pHead->_pNext;    while (pCur != pHead)    {        if (pCur->_data == data)        {            return pCur;        }        pCur = pCur->_pNext;    }    return NULL;}//销毁链表void DCLDestroy(PNode* ppHead){    PNode pCur = NULL;    assert(ppHead);    pCur = (*ppHead)->_pNext;    while (pCur != *ppHead)    {        pCur = pCur->_pNext;        free(pCur->_pPre);    }    free(pCur);    *ppHead = NULL;}