双向链表

#include<stdio.h>
#include<stdlib.h>

/*数据结构：存放数据的一种结构*/
/*结构体：秒速的是数据的结构单元*/
/*结构体复杂，但是当我们把单个结点拿出来分析，就不复杂了*/
struct   Node
{
     int   data;
     struct  Node*left;    /*左指针和右指针*/
     struct  Node*right;.
};

//创建节点
struct   Node*creatNode(int   data)
{
       struct   Node*newNode = (struct   Node*)malloc(sizeof(struct   Node));
       newNode->data = data;
       newNode ->left = newNode->right = NULL;
       return  newNode;
}

struct   List
{
       lint   size;
       struct  Node*firstNode;/*第一个与第二个结点*/
       struct   Node*lastNode;
}

struct   List * createList()
{
        struct   List*list = (struct   Node*)malloc(sizeof(struct   List));
        list->size = 0;
        list->firstNode = list -> lastNode = NULL;
        return  list;
}

//表头插入
void   insertNodeByHead(struct   List* list ,  int   data)
{
      struct    Node*newNode = createNode(data);
      if(list->firstNode == NULL)
      {
           list->firstNode = newNode;/*只有这个结点时，即使表头又是表尾*/
           list->lastNod = newNode;
           list->firstNode = newNode;
       }
       else
       {
            list->firstNode->left = newNode;
            newNode->right = list->firstNode;
            list->firstNode = newNode;/*表头法插入在这里只有两条线，即两个指针指向，另外两条为NULL*/
        }
        list->size++;
}

//表尾插入，和表头发插入一样
void   insertNodeByTail(struct   List*list, int   data)
/*和前面的单链表差不多*/
{
         struct   Node*newNode = createNode(data);
        if(list->lastNode == NULL)
        {
                  list -> firstNode = newNode;/*头结点*/
         }
         else
         {
                    list->lastNode->right = newNode;/*建立双向指定*/
                    newNode->left = list->lastNode;
          }
          list->lastNode=newNode;/*表尾移动*/
          list->size++;
}

//指定位置插入
void   isertNodeByAppoin(struct  List*list,int   data,int   posData)
{
      if(list->size == 0)//如果是空的，就是表头法插入
      {
              printf("链表为空，无法插入！");
              return;
       }
       else  if(list->firstNode->data == posData)/*第一个节点正好等于指定位点的数据，那就是表头法插入*/
       {
        insertNodeByHead(list,data);
        }
        else
        {
                  struct   Node*posNode = list->firstNode->right;
                  struct   Node*posNodeLeft = list->firstNode;
                  while(posNode !=NULL&&posNode->data != posData)
                  {
                             posNodeLeft = posNode;
                             posNode = posNode->right;
                    }
                    if(posNode == NULL)
                    {
                               printf("未找到相应位置，无法插入！");
                               return;
                      }
                      else
                      {
                                struct   Node*newNode = createNode(data);
                                 posNodeLeft->right = newNode;
                                 newNode->left = posNodeLeft;
                                   newNode->right = posNode;
                                   posNode ->left = newNode;
                        }
         }
}

//求大小，判断size是否为NULL
int  listSize(struct  List*list)                      /*其实现在我搞不懂这是干嘛的*/
{
     return   list->size;
}
int  emptyList(struct    List*list)
{
    if(list->size==0)
    return 0;
    else
    return1;
}

void   printListByRight(struct   List*list)
{
     if(list->size == 0)
     printf("无法打印，链表为空！")；
     else
     {
              struct  Node* pMove = list->firstNode; 
              while(pMove)
              {
                       printf("%d",pMove->data);
                       pMove = pMove->right;
               }
      }
      printf("\n");
}

void   printListByLeft(struct   List*list)
{
       if(list->size==0)
       printf("无法打印，链表为空！");
      else
      {
              struct   Node*pMove = list->lastNode;
              while(pMove)
              {
                          printf("%d",pMove->data);
                          pMove = pMove->left;
               }
       } 
       print("\n");
}

int   main()
{
      struct   List*list = createList();
      inserNodeByHead(list,3);
      inserNodeByHead(list,2);
      inserNodeByHead(list,1);
      printListByLeft(list);    //左往右插
      printListByRight(list);//右往左插
      insertNodeByAppoin(list,200,100);/*在100前面插入200*/
      printListByLeft(list);
      printListByRight(list);


    system("pause");
    return  0;
}