目录

一、结构定义

二、结点创建

三、头结点初始化

四、链表打印 

五、尾插

六、头插

七、尾删

八、头删

九、查找（返回结点）

十、任意位置插入

十一、任意位置删除

十二、利用LTInsert写尾插函数

十三、利用LTInsert写头插函数

十四、利用LTErase写尾删函数

十五、利用LTErase写头删函数

十六、销毁链表 

十七、测试代码

---

一、结构定义

//带头双向循环链表的结构定义
typedef int LTDataType;typedef struct ListNode {LTDataType val;struct LTNode* next;struct LTNode* prev;
}LTNode;

二、结点创建

//带头双向循环链表结点创建
LTNode* CreateLTNode(LTDataType x)
{LTNode* newnode = (LTNode*)malloc(sizeof(LTNode));if (newnode == NULL){perror("malLoc fail:");exit(-1);}newnode->val = x;newnode->next = NULL;newnode->prev = NULL;return newnode;
}

三、头结点初始化

//带头双向循环链表的初始化
LTNode* LTInit(LTNode* phead)
{phead = CreateLTNode(-1);phead->next = phead;phead->prev = phead;return phead;
}

四、链表打印 

//带头双向循环链表的打印
void LTPrint(LTNode* phead)
{assert(phead);LTNode* cur = phead->next;while (cur != phead){printf("%d<=>", cur->val);cur = cur->next;}printf("\n");
}

五、尾插

//带头双向循环链表的尾插
void LTPushBack(LTNode* phead, LTDataType x)
{assert(phead);LTNode* newnode = CreateLTNode(x);LTNode* tail = phead->prev;//尾指针//尾插tail->next = newnode;newnode->prev = tail;newnode->next = phead;phead->prev = newnode;}

六、头插

//带头双向循环链表的头插
void LTPushFront(LTNode* phead, LTDataType x)
{assert(phead);LTNode* newnode = CreateLTNode(x);LTNode* first = phead->next;newnode->next = first;first->prev = newnode;phead->next = newnode;newnode->prev = phead;
}

七、尾删

//带头双向循环链表的尾删
void LTPopBack(LTNode* phead)
{assert(phead);assert(phead->next != phead);//空链表不能删LTNode* tail1 = phead->prev;//尾1结点LTNode* tail2 = tail1->prev;//尾2结点tail2->next = phead;phead->prev = tail2;free(tail1);tail1 = NULL;
}

八、头删

//带头双向循环链表的头删
void LTPopFront(LTNode* phead)
{assert(phead);assert(phead->next != phead);//空链表不能删LTNode* first = phead->next;LTNode* second = first->next;free(first);first = NULL;phead->next = second;second->prev = phead;}

九、查找（返回结点）

//带头双向循环链表的查找
LTNode* LTFind(LTNode* phead, LTDataType x)
{assert(phead);LTNode* cur = phead->next;while (cur != phead){if (cur->val == x)return cur;elsecur = cur->next;}return NULL;
}

十、任意位置插入

如果插入位置是哨兵位，那么相当于尾插

如果插入位置是哨兵位的后一结点，那么相当于头插

//带头双向循环链表的任意位置插入
void LTInsert(LTNode* pos, LTDataType x)
{assert(pos);//插入位置必须有效LTNode* newnode = CreateLTNode(x);LTNode* posPrev = pos->prev;newnode->next = pos;pos->prev = newnode;posPrev->next = newnode;newnode->prev = posPrev;
}

十一、任意位置删除

如果删除位置是哨兵位的后一结点，那么相当于头删

如果删除位置是哨兵位的前一结点，那么相当于尾删

//带头双向循环链表的任意位置删除
void LTErase(LTNode* pos)
{assert(pos);LTNode* posPrev = pos->prev;LTNode* posNext = pos->next;posPrev->next = posNext;posNext->prev = posPrev;free(pos);
}

十二、利用LTInsert写尾插函数

//利用LTInsert写尾插函数
void LTPushBackInsert(LTNode* phead, LTDataType x)
{assert(phead);LTInsert(phead, x);
}

十三、利用LTInsert写头插函数

//利用LTInsert写头插函数
void LTPushFrontInsert(LTNode* phead, LTDataType x)
{assert(phead);LTInsert(phead->next, x);
}

十四、利用LTErase写尾删函数

//利用LTErase写尾删函数
void LTPopBackErase(LTNode* phead)
{assert(phead->next != phead);//链表为空不能删除LTErase(phead->prev);
}

十五、利用LTErase写头删函数

//利用LTErase写头删函数
void LTPopFrontErase(LTNode* phead)
{assert(phead->next != phead);LTErase(phead->next);
}

十六、销毁链表 

//销毁带头双向循环链表
void LTDestroy(LTNode* phead)
{assert(phead);LTNode* cur = phead->next;while (cur != phead){LTNode* tmp = cur;cur = cur->next;free(tmp);}free(phead);
}

十七、测试代码

void test01()
{//初始化哨兵位LTNode* plist = NULL;plist = LTInit(plist);//LTNode* plist = LTInit(plist);//尾插LTPushBack(plist, 1);LTPushBack(plist, 2);LTPushBack(plist, 3);LTPushBack(plist, 4);LTPushBack(plist, 5);LTPushBack(plist, 6);//头插LTPushFront(plist, 1);LTPushFront(plist, 2);LTPushFront(plist, 3);LTPushFront(plist, 4);LTPushFront(plist, 5);LTPushFront(plist, 6);//打印LTPrint(plist);//尾删LTPopBack(plist);LTPopBack(plist);LTPopBack(plist);//打印LTPrint(plist);//头删LTPopFront(plist);LTPopFront(plist);LTPopFront(plist);//打印LTPrint(plist);//查找值为2的结点并在该位置插入值为10的结点LTNode* pos1 = LTFind(plist, 2);LTInsert(pos1, 10);//打印LTPrint(plist);//查找值为3的结点并删除该结点LTNode* pos2 = LTFind(plist, 3);LTErase(pos2);//打印LTPrint(plist);//尾插LTPushBackInsert(plist, 1);LTPushBackInsert(plist, 2);LTPushBackInsert(plist, 3);LTPushBackInsert(plist, 4);//打印LTPrint(plist);//头插LTPushFrontInsert(plist, 1);LTPushFrontInsert(plist, 2);LTPushFrontInsert(plist, 3);LTPushFrontInsert(plist, 4);//打印LTPrint(plist);//尾删LTPopBackErase(plist);LTPopBackErase(plist);LTPopBackErase(plist);//打印LTPrint(plist);//头删LTPopFrontErase(plist);LTPopFrontErase(plist);LTPopFrontErase(plist);//打印LTPrint(plist);//销毁链表//LTDestroy(plist);//plist=NULL;}int main()
{test01();return 0;
}