双链表的实现（数据结构）

链表总体可以分为三大类

一、无头和有头

二、单向和双向

三、循环和不循环

从上面分类得知可以组合成8种不同类型链表，其中单链表最为简单，双联表最为复杂，两种链表都实现后其余链表都不成问题。

我们前期博客已将完成了单向无头不循环链表（单链表）的实现，本期博客我们实现双向有头循环链表的实现。

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说明：

因为此双链表有头结点，（头结点不存储任何有效数据，双链表中只有头结点时为空链表）

因此我们无需修改头结点的地址，只需要改变头结点中前驱指针和后面指针的指向即可，所以传参时只需要传头结点的地址即可。

代码实现：

List.h

#pragma once
#include<stdio.h>
#include<stdlib.h>
#include<assert.h>
#include<stdbool.h>typedef int LTDataType;typedef struct ListNode
{struct ListNode* prev;struct ListNode* next;LTDataType data;
}LTNode;//void LTInit(LTNode** pphead);
LTNode* LTInit();
void LTDestroy(LTNode* phead);//为了保持接口一致性，需要在外部将phead置空。//保留头节点其他的删去
void LTClear(LTNode* phead);
LTNode* BuyNode(LTDataType x);void LTPrint(LTNode* phead);
bool LTEmpty(LTNode* phead);//判断是否为空void LTPushBack(LTNode* phead, LTDataType x);
void LTPopBack(LTNode* phead);void LTPushFront(LTNode* phead, LTDataType x);
void LTPopFront(LTNode* phead);
//在pos位置之后插入数据
void LTInsert(LTNode* pos, LTDataType x);
void LTErase(LTNode* pos);LTNode* LTFind(LTNode* phead, LTDataType x);

List.c

#define _CRT_SECURE_NO_WARNINGS 1
#include"List.h"LTNode* LTInit()
{LTNode* phead = BuyNode(-1);return phead;
}LTNode* BuyNode(LTDataType x)
{LTNode* newnode = (LTNode*)malloc(sizeof(LTNode));if (newnode == NULL){perror("malloc fail!");exit(1);}newnode->prev = newnode->next = newnode;newnode->data = x;return newnode;
}void LTDestroy(LTNode* phead)
{//哨兵位不能为空assert(phead);LTNode* pcur = phead->next;while (pcur!=phead){LTNode* next = pcur->next;free(pcur);pcur = next;}free(phead);phead = NULL;
}
//清除链表的内容
void LTClear(LTNode* phead)
{assert(phead);LTNode* pcur = phead->next;while (pcur != phead){LTNode* next = pcur->next;free(pcur);pcur = next;}phead->next = phead;phead->prev = phead;
}
void LTPrint(LTNode* phead)
{//链表不能为空assert(phead);LTNode* pcur = phead->next;while (pcur!=phead){printf("%d->",pcur->data);pcur = pcur->next;}printf("\n");
}
bool LTEmpty(LTNode* phead)
{if (phead->next = phead){return true;}else{return false;}
}void LTPushBack(LTNode* phead, LTDataType x)
{assert(phead);LTNode* newnode = BuyNode(x);LTNode* ptail = phead->prev;ptail->next = newnode;newnode->prev = ptail;newnode->next = phead;phead->prev = newnode;
}
void LTPopBack(LTNode* phead)
{assert(phead);//链表不能为空assert(phead->next!=phead);LTNode* ptail = phead->prev;LTNode* prev = ptail->prev;phead->prev = prev;prev->next = phead;free(ptail);ptail = NULL;
}void LTPushFront(LTNode* phead, LTDataType x)
{assert(phead);LTNode* newnode = BuyNode(x);LTNode* next = phead->next;phead->next = newnode;newnode->prev = phead;newnode->next = next;next->prev = newnode;}
void LTPopFront(LTNode* phead)
{assert(phead);assert(phead->next != phead);LTNode* pos = phead->next;LTNode* next = pos->next;phead->next = next;next->prev = phead;free(pos);pos = NULL;
}
//在pos位置之后插入数据
void LTInsert(LTNode* pos, LTDataType x)
{assert(pos);LTNode* newnode = BuyNode(x);LTNode* next = pos->next;//pos newnode nextpos->next = newnode;newnode->prev = pos;newnode->next = next;next->prev = newnode;
}
void LTErase(LTNode* pos)
{assert(pos);LTNode* prev = pos->prev;LTNode* next = pos->next;prev->next = next;next->prev = prev;free(pos);pos = NULL;
}
LTNode* LTFind(LTNode* phead, LTDataType x)
{assert(phead);LTNode* pcur = phead->next;while (pcur->data!=x && pcur!=phead){pcur = pcur->next;}if (pcur->data == x){return pcur;}else{return NULL;};
}

test.c

#define _CRT_SECURE_NO_WARNINGS 1
#include"List.h"int main()
{LTNode* phead = LTInit();if(LTEmpty(phead)){printf("链表为空\n");}LTPushBack(phead,1);LTPushBack(phead,2);LTPushBack(phead,3);LTPushBack(phead,4);LTPrint(phead);LTPopBack(phead);LTPopBack(phead);LTPrint(phead);LTPopFront(phead);LTPrint(phead);LTPushFront(phead,100);LTPushFront(phead,200);LTPushFront(phead,300);LTPrint(phead);LTNode* ret= LTFind(phead,200);if (ret){LTErase(ret);}else{printf("未找到，无法删除\n");}LTPrint(phead);LTNode* ret2 = LTFind(phead, 2);if (ret2){LTInsert(ret2, 3);}else{printf("未找到，无法插入\n");}LTPrint(phead);LTDestroy(phead);phead = NULL;return 0;
}