双向循环链表

#include<stdio.h>
#include<stdlib.h>
struct   Node
{
       int   data;
       struct   Node*right;
       struct   Node*left;
};

//创建链表
struct   Node*createList()
{
      struct   Node*headNode = (struct   Node*)malloc(sizeof(struct  Node));
      headNode->right = headNode->left = headNode;/*刚开始时只有一个结点，所以都指向自身*/
      return  headNode;
}

//创建结点
struct   Node*createNode(int    data)
{
       struct   Node*newNode = (struct   Node*)malloc(sizeof(struct   Node));
       newNode->left = newNode->right = NULL;/*先令左右指针为空*/
       newNode->data=data;
       return   newNode;
}

//插入
void   insertNodeByTail(struct   Node*headNode, int   data)
{
        struct   Node* newNode = createNode(data);
        struct   Node* tailNode = headNode->left;/*因为链表是循环的，所以头结点和尾结点是互相连接的，在这里用tailNode作为尾结点*/
        tailNode->right = newNode;
        newNode->left = tailNode;
        newNode->right = headNode;
        headNode->left = newNode;
}

//指定位置插入
void   insertNodeByAppoin(struct      Node*headNode,int   data,int     posData)
{
      if(headNode->left == headNode->right)
      {
               printf("链表为空，无法指定位置插入");
               return;        
       }
      else
      {
      struct   Node*posNode = headNode->right;
      struct   Node*posNodeLeft = headNode;
      while(posNode->data != posData)
           {
                    posNodeLeft = posNode;
                    posNode=posNodeLeft->right;
                    if(posNode == headNode)/*这里是posNode经历了一个轮回，还没有找到*/
                    { 
                              printf("没有找到指定位置，无法插入！");
                     }
            }
            struct    Node*newNode = createNode(data);
            posNodeLeft->right = newNode;
            newNode->left = posNodeLeft;
            posNode->left = newNode;
            newNode->right = posNode;
     }
}

//打印
void   printListRight(struct   Node* headNode)/*从右往左打印*/
{
    if(headNode->left == headNode->right)
    {
            printf("表头为空，无法打印！")；
            return;/*return表示返回为空，return  0 和return   1表示返回整形*/
      }
      struct    Node*pMove = headNode->right;
      while(pMove != headNode)
      {
               printf("%d\t",pMove->data);
               pMove=pMove->right; 
       }
       printf("\n");
}

/*从左往右打印*/
void   printListLeft(struct   Node*headNode)
{
      if(headNode->left ==headNode->right)
      {
               printf("表头为空，无法打印！");
               return;
       }
       struct   Node*pMove = headNode->left;
       while(pMove!=headNode)
       {
                printf("%d\t",pMove->data);
                pMove=pMove->left;
         }
         printf("\n");
}


int   main()
{
      struct   Node*list = createList();
      insertNodeByTail(list,3);
      insertNodeByTail(list,2);
      insertNodeByTail(list,1);
      printListRinght(list);
       printListLeft(list);

       system("pause");
        return   0;
}