一：需求简述，C语言编写一个双向链表 （三）

   需求简述：用C语言编写一个 双向链表
    需要重视基础

代码v1.0： v1-0.rar  

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

typedef char ElemType;
typedef struct _list
{
    ElemType data;
    struct _list *prior;   ##注意原先，我是写成 int*prior 的。
    struct _list *next;
    int length; //获取链表结点数
}LIST;

LIST *init_list(void)
{
    LIST *l=NULL;
    l=(LIST *)malloc(sizeof(LIST)); //申请 head结点 *prior *next 地址空间
    if(l==NULL)
        exit(1);
    l->prior=l->next=NULL;
    l->data=0;
    l->length=0; //初始化 链表结点数=0
    return l;
}

int insert_elem(LIST *l,int i,ElemType *e)
{
    LIST *list=l;
    LIST *new=NULL;
    int j=1;

    if(i<1||i>l->length+1)
        return 1;

    new=(LIST *)malloc(sizeof(LIST));
    if(new==NULL)
    {
        free(new);
        exit(1);
    }
    new->data=*e;   //初始化 结点数据
    new->prior=NULL;
    new->next=NULL;

    while(j<i)  //定位到 要插入的 前一个结点 i-1
    {
        list=list->next;
        j++;
    }
/* M        N
      NEW       三个结点，NEW为要插入的结点
*/
    new->next=list->next;   //NEW->next=N;
    new->prior=list;        //NEW->prior=M
    if(list->next!=NULL) //如果不是最后一个结点
        new->next->prior=new;  //N->prior=NEW
        // 如果是最后一个结点，         N后没有结点
    list->next=new;             //M->next=NEW;

    ++l->length;
    return 0;
}

int delete_elem(LIST *l,int i)
{
    LIST *list=l;
    LIST *tmp=NULL;
    int j=1;
    if(i<1||i>l->length)
        return 1;

    while(j<i)    //定位到 要删除 i的前一个 i-1 结点
    {
        j++;
        list=list->next;
    }

    tmp=list->next;  //指向要删除的结点
    list->next=tmp->next;
    if(tmp->next!=NULL)//tmp 不是最后结点
        tmp->next->prior=list;
    free(tmp);
    --l->length;
    return 0;
}

int main()
{
    ElemType ch1='a';
    ElemType ch2='b';
    ElemType ch3='c';
    LIST *list;
    list=init_list();

        insert_elem(list,1,&ch1);    插入节点
        insert_elem(list,1,&ch2);
    insert_elem(list,3,&ch3);
    printf("1th data is %c\n",list->next->data);
    printf("2th data is %c\n",list->next->next->data);
    printf("2th data is %c\n",list->next->next->next->data);
    printf("length = %d\n",list->length);

    printf("delete node 1...\n");  删除节点
    delete_elem(list,1);
    printf("1th data is %c\n",list->next->data);
    printf("2th data is %c\n",list->next->next->data);
    printf("length = %d\n",list->length);

    printf("delete node 2...\n");  删除节点
    delete_elem(list,2);
    printf("1th data is %c\n",list->next->data);
    printf("length = %d\n",list->length);

    return 0;
}

ywx@yuweixian:~/yu/professional/1$ ./link
1th data is b
2th data is a
2th data is c
length = 3
delete node 1...
1th data is a
2th data is c
length = 2
delete node 2...
1th data is a
length = 1