数据结构之双向链表的实现

*****双向链表的实现*****

双链表就可以看成两个单链表组合成的，只是相比单链表而言，它能从两个方向进行遍历链表，目前还不知道这有什么
优势，因为当我们想查找一个元素时，并不知道一个有序的链表里面这个被查找的元素离哪一边较近。

（1）双链表的结构与单链表有点不一样，它要保证从链表的任意一端都能遍历链表，所以下面是双链表里面的结点的结构：

typedef structdouList{               struct douList *prior;               struct douList *next;               int data;}DouList;

（2）双向链表的创建，并初始化：

DouList *Creat_List(){               DouList *root = NULL;               DouList *pre = NULL;               DouList *cur = NULL;               int data = 0;               int i = 0;                 root = (DouList*)malloc(sizeof(DouList));               if(NULL == root)               {                               printf("ERROR:Can't malloc the root.\n");                               exit(ERROR);               }               root->next = NULL;               root->prior = NULL;                 pre = root;               while(++i <= 10)               {                               cur = (DouList*)malloc(sizeof(DouList));                               if(NULL == cur)                               {                                              printf("ERROR:Can't malloc the current List\n");                                              exit(ERROR);                               }                                 //init the cur                               cur->next =NULL;                               cur->prior =NULL;                               cur->data =2*i - 1;                                 //connect theDoubly Linked List                               pre->next =cur;                               cur->next =NULL;                               if(pre == root)                               {                                              cur->prior= NULL;                                              pre->prior= NULL;                                              pre->prior= cur;                               }                               else                               {                                              root->prior= cur;                                              cur->prior= pre;                               }                               pre = cur;               }                 return root;}

（2）双向链表的遍历：

<1>正向遍历，即以next方向遍历：

voidShow_NextList(DouList *root){               DouList *pre = root->next;                 printf("This is the doublylinked list in the next order;\n");               while(NULL != pre)               {                               printf("%d\n",pre->data);                               pre =pre->next;               }}

<2>反向遍历，即以prior方向遍历：

voidShow_PriorList(DouList *root){               DouList *pre = root->prior;                 printf("This is the doublylinked list in the prior order;\n");               while(NULL != pre)               {                               printf("%d\n",pre->data);                               pre =pre->prior;               }}

（3）查找结点，同样这里只实现返回结点：

<1>正向查找：

DouList*Find_NextList(DouList *root){               DouList *cur = root->next;               int data;                 printf("Enter a data youwant to find in next order:\n");               scanf("%d",&data);                 while(NULL != cur)               {                               if(data ==cur->data)                               {                                              returncur;                               }                               cur =cur->next;               }                 return NULL;}

<2>反向查找：

DouList*Find_PriorList(DouList *root){               DouList *cur = root->prior;               int data;                 printf("Enter a data youwant to find in prior order:\n");               scanf("%d",&data);                 while(NULL != cur)               {                               if(data ==cur->data)                               {                                              returncur;                               }                               cur =cur->prior;               }                 return NULL;}

（4）插入新结点：（仅实现了next方向的插入）

DouList*Insert_List(DouList *root){               DouList *cur = root->next;               DouList *pre = root;               int data = 0;               DouList *newList = NULL;                 printf("Enter the data youwant to insert:\n");               scanf("%d",&data);                 newList = (DouList*)malloc(sizeof(DouList));               if(NULL == newList)               {                               printf("ERROR:Can't malloc the new List.\n");                               exit(ERROR);               }                 newList->data = data;               newList->next = NULL;               newList->prior = NULL;                 while(NULL != cur->next)               {                               //find thelocation which need to be inserted                               if(data < cur->data)                               {                                              //ifthe new List in the front of the first List(except the root)                                              if(root->next== cur)                                              {                                                             root->next= newList;                                                             newList->next= cur;                                                             newList->prior= NULL;                                                             cur->prior= newList;                                              }                                              //ifthe new List in the front of the last List                                              //whenin the order of next                                              else                                              {                                                             pre->next= newList;                                                             newList->next= cur;                                                             newList->prior= pre;                                                             cur->prior= newList;                                              }                                                break;                               }                               //move thepointer to the doubly linked list                               else                               {                                              pre= cur;                                              cur= cur->next;                               }               }                 if(NULL == cur->next)               {                               //insert the newList in the front of last List                               if(data <cur->data)                               {                                              pre->next= newList;                                              newList->next= cur;                                              cur->prior= newList;                                              newList->prior= pre;                               }                               //insert the newList in the last List                               else                               {                                              cur->next= newList;                                              newList->next= NULL;                                              newList->prior= cur;                                              root->prior= newList;                               }               }                 //insert successe               return newList;}

（5）删除结点：（仅实现了以next的方向）

DouList*Delete_List(DouList *root){               DouList *cur = root->next;               DouList *pre = root;               DouList *deleteList = NULL;               int data;                 printf("Enter a data youwant to delete:\n");               scanf("%d",&data);                 while(NULL != cur->next)               {                               if(data ==cur->data)                               {                                              deleteList= cur;                                                //ifthe list to delete is in the first List(except the root)                                              if(root->next== cur)                                              {                                                             cur->next->prior= NULL;                                                             root->next= cur->next;                                              }                                              //ifthe list to delete isn't in the first List(except the root)                                              else                                              {                                                             pre->next= cur->next;                                                             cur->next->prior= pre;                                              }                                              free(cur);                                                                                           //thedeleteList is connected with the cur                                              //whencur was free,deleteList will become shakable                                              //shouldinit the deleteList to let the return's use                                              deleteList->next= NULL;                                              deleteList->prior= NULL;                                              deleteList->data= data;                                                                                           returndeleteList;                               }                               else                               {                                              pre= cur;                                              cur= cur->next;                               }               }                 //when the list to delete is inthe last List               if(data == cur->data)               {                               deleteList = cur;                               pre->next =NULL;                               root->prior =pre;                                                             free(cur);                                 deleteList->next= NULL;                               deleteList->prior= NULL;                               deleteList->data= data;                               returndeleteList;               }                 return NULL;}

*****总结*****

这次能够实现这两种链表的功能，这要靠两种工具：
（1）严老师的《数据结构》一书，里面提供了链表实现的各种的思想基础
（2）调试，以前总看别人写的东西都说C程序员必须学会调试,这次实现这些东西的一大利器
就是它了,初次使用调试来解决指针问题,真心觉得它的前途无限。