无头单向不循环链表和带头双向循环链表的创建
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前言：
接下来我们将会了解最基础的链表--->单链表
以及最方便也是最爽的链表--->带头双向循环链表。
若有看不懂之处，可画图或者借鉴这里：反转单链表，对于数据结构而言，无非就是增删查改，当我们能够熟练应用以及画图后，其OJ题和以下代码都是小卡拉米。
无头单向不循环链表
单链表图：
头文件：
#include <stdio.h> #include <stdlib.h> #include <assert.h>typedef int DataType;typedef struct STLNode {DataType data;struct STLNode* next; }STLNode;void STL_Print(STLNode* phead); void STL_PushBack(STLNode** pphead, DataType x); void STL_PushFront(STLNode** pphead, DataType x); void STL_PopBack(STLNode** pphead); void STL_PopFront(STLNode** pphead); STLNode* STL_Find(STLNode* phead, DataType x); void STL_InsertAfter(STLNode* pos, DataType x); void STL_EraseAfter(STLNode* pos); void STL_Destroy(STLNode** pphead);Test文件：
#include "STLNode.h"void Test1(STLNode* phead);int main() {STLNode* plist = NULL;Test1(plist);return 0; }void Test1(STLNode* phead) {STL_PushBack(&phead, 1);STL_PushBack(&phead, 2);STL_PushBack(&phead, 3);STL_Print(phead);STL_PushFront(&phead, 11);STL_PushFront(&phead, 22);STL_PushFront(&phead, 33);STL_Print(phead);STLNode* ret = STL_Find(phead, 1);STL_InsertAfter(ret, 666);STL_Print(phead);STL_EraseAfter(ret);STL_Print(phead);STL_Destroy(&phead);STL_Print(phead);//STL_PopBack(&phead);//STL_PopBack(&phead);//STL_Print(phead);//STL_PopFront(&phead);//STL_PopFront(&phead);//STL_Print(phead);}函数源文件：
对于以下函数中部分有对phead和pphead的检查，部分没有，原因是这样的：
对于是否需要对其进行断言，我们是要看他为NULL时合不合理，合理就不断言，不合理就断言，例如STL_Printf函数中，当phead为NULL时，说明该链表是空的，直接打印NULL就可以，这是很合理的。而对于STL_PushBack函数来说，phead为NULL同样合理，因为phead为NULL我们尾插其实也就相当于头插，很合理，但是对于pphead来说，他作为plist的地址，就算plist为NULL，pphead是不应该为NULL的，所以他为NULL就非常不合理，我们要对其进行断言检查。
#include "STLNode.h"void STL_Print(STLNode* phead) {while (phead){printf("%d->", phead->data);phead = phead->next;}printf("NULL\n");}STLNode* Malloc(DataType x) {STLNode* temp = (STLNode*)malloc(sizeof(STLNode));if (temp == NULL){perror("malloc fail");exit(-1);}temp->data = x;temp->next = NULL;return temp; }void STL_PushBack(STLNode** pphead, DataType x) {assert(pphead);STLNode* temp = Malloc(x);if (*pphead == NULL){*pphead = temp;}else{STLNode* cur = *pphead;while (cur->next != NULL){cur = cur->next;}cur->next = temp;} }void STL_PushFront(STLNode** pphead, DataType x) {assert(pphead);STLNode* temp = Malloc(x);temp->next = *pphead;*pphead = temp;}void STL_PopBack(STLNode** pphead) {assert(pphead);assert(*pphead);STLNode* cur = *pphead;STLNode* temp = *pphead;if (cur->next == NULL){free(cur);*pphead = NULL;}else{while (cur->next){temp = cur;cur = cur->next;}free(cur);temp->next = NULL;}}void STL_PopFront(STLNode** pphead) {assert(pphead);assert(*pphead);STLNode* cur = *pphead;*pphead = (*pphead)->next;free(cur);}STLNode* STL_Find(STLNode* phead, DataType x) {if (phead == NULL){printf("NULL\n");return;}while (phead != NULL){if (phead->data == x){return phead;}phead = phead->next;}printf("Can not find\n");return; }void STL_InsertAfter(STLNode* pos, DataType x) {assert(pos);STLNode* temp = Malloc(x);temp->next = pos->next;pos->next = temp;}void STL_EraseAfter(STLNode* pos) {assert(pos);assert(pos->next);STLNode* cur = pos->next;pos->next = pos->next->next;free(cur); }void STL_Destroy(STLNode** pphead) {assert(pphead);if (*pphead == NULL){return;}STLNode* temp = *pphead;STLNode* cur = *pphead;while (temp){cur = temp->next;free(temp);temp = cur;}*pphead = NULL; }
带头双向循环链表
图：
头文件：
这个链表最爽的地方在于，他可以很轻松地找到尾，不管是尾插还是头插都非常爽，非常方便，如果我们想在半小时内写完这个链表，那么就可以对尾插和头插复用LTInsert函数，对于尾删和头删复用LTErase函数,也就是说，这两个函数是核心函数，有了他们，迅速写完该链表成为现实。
尾插的复用：LTInsert(phead,x);
头插的复用：LTInsert(phead->next,x);
尾删的复用：LTErase(phead->prev);
头删的复用：LTErase(phead->next);
#include <stdio.h> #include <stdlib.h> #include <assert.h>typedef int DataType;typedef struct LTNode {DataType data;struct LTNode* prev;struct LTNode* next; }LTNode;LTNode* Init(); LTNode* Malloc(DataType x); LTNode* LTFind(LTNode* phead, DataType x); void LTPrintf(LTNode* phead); void LTPushBack(LTNode* phead, DataType x); void LTPopBack(LTNode* phead); void LTPushFront(LTNode* phead, DataType x); void LTPopFront(LTNode* phead); void LTInsert(LTNode* pos, DataType x); //在pos位置前插入节点 void LTErase(LTNode* pos); //删除pos位置节点 void LTDestroy(LTNode* phead);Test文件：
#define _CRT_SECURE_NO_WARNINGS 1 #include "LTNode.h"void Test1();int main() {Test1();return 0; }void Test1() {LTNode* plist = NULL;plist = Init();LTPushBack(plist, 1);LTPushBack(plist, 2);LTPushBack(plist, 3);LTPushBack(plist, 4);LTPushBack(plist, 5);LTPushBack(plist, 6);LTPrintf(plist);LTPopBack(plist);LTPopBack(plist);LTPopBack(plist);LTPrintf(plist);LTPushFront(plist, 10);LTPushFront(plist, 20);LTPushFront(plist, 30);LTPrintf(plist);LTPopFront(plist);LTPrintf(plist);LTNode *pos = LTFind(plist, 10);LTInsert(pos, 66);LTPrintf(plist);LTErase(pos);LTPrintf(plist);LTDestroy(plist);plist = NULL;}函数源文件：
#define _CRT_SECURE_NO_WARNINGS 1 #include "LTNode.h"LTNode* Malloc(DataType x) {LTNode* newnode = (LTNode*)malloc(sizeof(LTNode));if (newnode == NULL){perror("malloc fail");exit(-1);}newnode->data = x;return newnode; }LTNode* Init() {LTNode* newnode = Malloc(0);newnode->next = newnode;newnode->prev = newnode;return newnode; }void LTPrintf(LTNode* phead) {assert(phead);printf("phead<=>");LTNode* cur = phead->next;while (cur != phead){printf("%d<=>", cur->data);cur = cur->next;}putchar('\n'); }void LTPushBack(LTNode* phead, DataType x) {assert(phead);LTNode *newnode = Malloc(x);LTNode* tail = phead->prev;tail->next = newnode;newnode->prev = tail;newnode->next = phead;phead->prev = newnode;}void LTPopBack(LTNode* phead) {assert(phead);assert(phead->next != phead);LTNode* tail = phead->prev;LTNode* newtail = tail->prev;newtail->next = phead;phead->prev = newtail;free(tail); }void LTPushFront(LTNode* phead, DataType x) {assert(phead);LTNode* newnode = Malloc(x);LTNode* old_next = phead->next;phead->next = newnode;newnode->prev = phead;newnode->next = old_next;old_next->prev = newnode;}void LTPopFront(LTNode* phead) {assert(phead);assert(phead->next != phead);LTNode* del = phead->next;phead->next = del->next;del->next->prev = phead;free(del); }LTNode* LTFind(LTNode* phead, DataType x) {assert(phead);LTNode* cur = phead->next;while (cur != phead){if (cur->data == x){return cur;}cur = cur->next;}printf("nothing!\n");return NULL; }void LTInsert(LTNode* pos, DataType x) {assert(pos);LTNode* newnode = Malloc(x);LTNode* posprev = pos->prev;posprev->next = newnode;newnode->prev = posprev;newnode->next = pos;pos->prev = newnode; }void LTErase(LTNode* pos) {assert(pos);LTNode* posprev = pos->prev;LTNode* posnext = pos->next;posprev->next = posnext;posnext->prev = posprev;free(pos); }void LTDestroy(LTNode* phead) {assert(phead);LTNode* cur = phead->next;while (cur != phead){LTNode* next = cur->next;free(cur);cur = next;}free(cur); }