1.链表的分类

实际中链表的结构非常多样，以下情况组合起来就有8种链表结构：

（1）单向或者双向

（2）带头或者不带头

（3）循环或者非循环

 虽然有这么多的链表的结构，但是我们实际中最常用还是两种结构：

 1. 无头单向非循环链表：结构简单，一般不会单独用来存数据。实际中更多是作为其他数据结构的子结构，如哈希桶、图的邻接表等等。

2. 带头双向循环链表：结构最复杂，一般用在单独存储数据。实际中使用的链表数据结构，都是带头双向循环链表。

2.无头单向非循环链表的实现

// 1、无头+单向+非循环链表增删查改实现
typedef int SLTDateType;
typedef struct SListNode
{SLTDateType data;struct SListNode* next;
}SListNode;// 动态申请一个节点
SListNode* BuySListNode(SLTDateType x);
// 单链表打印
void SListPrint(SListNode* plist);
// 单链表尾插
void SListPushBack(SListNode** pplist, SLTDateType x);
// 单链表的头插
void SListPushFront(SListNode** pplist, SLTDateType x);
// 单链表的尾删
void SListPopBack(SListNode** pplist);
// 单链表头删
void SListPopFront(SListNode** pplist);
// 单链表查找
SListNode* SListFind(SListNode* plist, SLTDateType x);
// 单链表在pos位置之后插入x
void SListInsertAfter(SListNode* pos, SLTDateType x);
// 单链表删除pos位置之后的值
void SListEraseAfter(SListNode* pos);

// 1、无头+单向+非循环链表增删查改实现
SListNode* BuySListNode(SLTDateType x)
{SListNode* tmp = (SListNode*)malloc(sizeof(SListNode));if (tmp == NULL){printf("无法给节点开辟空间\n");return NULL;}else{tmp->data = x;tmp->next = NULL;return tmp;}
}

// 单链表打印
void SListPrint(SListNode* plist)
{SListNode* head = plist;while (head != NULL){printf("%d ", head->data);head = head->next;}
}

// 单链表尾插
void SListPushBack(SListNode** pplist, SLTDateType x)
{SListNode* newnode = BuySListNode(x);if ( *pplist== NULL){*pplist = newnode;}else{SListNode* tail = *pplist;while (tail->next != NULL){tail = tail->next;}tail->next = newnode;}
}

// 单链表的尾删
void SListPopBack(SListNode** pplist)
{assert(*pplist);SListNode* cur = *pplist;SListNode* prev = NULL;if (cur->next == NULL){free(cur);*pplist = NULL;}else{while (cur->next != NULL){prev = cur;cur = cur->next;}free(cur);prev->next = NULL;}
}

// 单链表的头插
void SListPushFront(SListNode** pplist, SLTDateType x)
{SListNode* newnode = BuySListNode(x);if (*pplist == NULL){*pplist = newnode;}else{newnode->next = *pplist;*pplist = newnode;}
}

// 单链表头删
void SListPopFront(SListNode** pplist)
{assert(*pplist);SListNode* cur = *pplist;if ((*pplist)->next == NULL){free(*pplist);*pplist = NULL;}else{cur = cur->next;free(*pplist);*pplist = cur;}
}

// 单链表查找
SListNode* SListFind(SListNode* plist, SLTDateType x)
{assert(plist);while (plist != NULL){if (plist->data == x){return plist;}plist = plist->next;}return NULL;
}

// 单链表在pos位置之后插入x
void SListInsertAfter(SListNode* pos, SLTDateType x)
{assert(pos);SListNode* newnode = BuySListNode(x);newnode->next = pos->next;pos->next = newnode;
}

// 单链表删除pos位置之后的值
void SListEraseAfter(SListNode* pos)
{assert(pos);if (pos->next == NULL){printf("后面无数据\n");return;}else{SListNode* prev = pos;SListNode* cur = pos->next;prev->next = cur->next;free(cur);cur = NULL;}}

3. 带头双向循环链表

// 2、带头+双向+循环链表增删查改实现
typedef int LTDataType;
typedef struct ListNode 
{ListDateType val;struct ListNode* prev;struct ListNode* next;
}ListNode;	//初始化双向链表
ListNode* ListInit(ListNode* phead);
//双向链表打印
void ListPrint(ListNode* phead);
// 创建返回链表的头结点.
ListNode* BuyList(ListDateType x);
//双向链表尾插
void ListPushBack(ListNode* phead,ListDateType x);
//双向链表尾删
void ListPopBack(ListNode* phead);
//双向链表头插
void ListPushFront(ListNode* phead, ListDateType x);
//双向链表头删
void ListPopFront(ListNode* phead);
//双向链表查找
ListNode* ListFind(ListNode* pHead, ListDateType x);
//在pos之前插入
void ListInsert(ListNode* pos, ListDateType x);
//删除pos位置
void ListErase(ListNode* pos);

//初始化双向链表
ListNode* ListInit(ListNode* phead)
{phead = BuyList(0);phead->next = phead;phead->prev = phead;return phead;
}

//双向链表打印
void ListPrint(ListNode* phead)
{ListNode* cur = phead->next;while (cur != phead){printf("%d ", cur->val);cur = cur->next;}}

// 创建返回链表的头结点
ListNode* BuyList(ListDateType x)
{ListNode* newnode = (ListNode*)malloc(sizeof(ListNode));if (newnode == NULL){printf("BuyList fail\n");exit(-1);}newnode->val = x;newnode->next = NULL;newnode->prev = NULL;return newnode;
}

//双向链表尾插
void ListPushBack(ListNode* phead, ListDateType x)
{assert(phead);ListNode* newnode = BuyList(x);ListNode* tail = phead->prev;tail->next = newnode;phead->prev = newnode;newnode->next = phead;newnode->prev = tail;
}

//双向链表尾删
void ListPopBack(ListNode* phead)
{assert(phead->next != phead);ListNode* tail = phead->prev;ListNode* prev = tail->prev;phead->prev = prev;prev->next = phead;free(tail);tail = NULL;
}

//双向链表头插
void ListPushFront(ListNode* phead, ListDateType x)
{assert(phead);ListNode* newnode = BuyList(x);ListNode* head = phead->next;phead->next = newnode;head->prev = newnode;newnode->next = head;newnode->prev = phead;
}

//双向链表头删
void ListPopFront(ListNode* phead)
{assert(phead);assert(phead->next != phead);ListNode* head = phead->next;ListNode* next = head->next;phead->next = next;next->prev = phead;free(head);head = NULL;
}

//双向链表查找
ListNode* ListFind(ListNode* phead, ListDateType x)
{assert(phead);assert(phead->next != phead);ListNode* pos = phead->next;while (pos != phead){if (pos->val == x){return pos;}pos = pos->next;}return NULL;
}

//在pos之前插入
void ListInsert(ListNode* pos, ListDateType x)
{assert(pos);ListNode* newnode = BuyList(x);ListNode* prev = pos->prev;prev->next = newnode;pos->prev = newnode;newnode->prev = prev;newnode->next = pos;
}

//删除pos位置
void ListErase(ListNode* pos)
{assert(pos);ListNode* prev = pos->prev;ListNode* next = pos->next;prev->next = next;next->prev = prev;free(pos);pos = NULL;
}