双链表的基本操作

#include <stdio.h>
#include <stdlib.h>
typedef int ElemType;
typedef struct DNode{
    ElemType data;
    struct DNode *prior,*next;
}DNode,*DLinkList;
//双向链表头插法
DLinkList Dlist_head_insert(DLinkList &DL)
{
    DNode *s;int x;
    //带头结点的链表,不带头结点
    DL=(DLinkList)malloc(sizeof(DNode));
    DL->next=NULL;
    DL->prior=NULL;
    //从标准输入读取数据
    scanf("%d",&x);
    //3 4 5 6 7 9999
    while(x!=9999){
        //申请一个空间空间，强制类型转换
        s=(DLinkList)malloc(sizeof(DNode));
        s->data=x;
        s->next=DL->next;
        //插入第一个结点时，不需要这一步操作
        if(DL->next!=NULL){
            DL->next->prior=s;
        }
        s->prior=DL;
        DL->next=s;
        scanf("%d",&x);//读取标准输入
    }
    return DL;
}
//双向链表尾插法
DLinkList Dlist_tail_insert(DLinkList &DL)
{
    int x;
    //带头节点的链表
    DL=(DLinkList)malloc(sizeof(DNode));
    DNode *s,*r=DL;
    DL->prior=NULL;
    //3 4 5 6 7 9999
    scanf("%d",&x);
    while(x!=9999){
        s=(DNode*)malloc(sizeof(DNode));
        s->data=x;
        r->next=s;
        s->prior=r;
        //r指向新的表尾结点
        r=s;
        scanf("%d",&x);
    }
    //尾结点的next指针赋值为NULL
    r->next=NULL;
    return DL;
}
//按序号查找结点值
DNode *GetElem(DLinkList DL,int i)
{
    int j=1;
    DNode *p=DL->next;
    if(i==0) return DL;
    if(i<1)    return NULL;
    while(p&&j<i){
        p=p->next;
        j++;
    }
    return p;
}
//新结点插入第i个位置
bool DListFrontInsert(DLinkList DL,int i,ElemType e)
{
    DLinkList p=GetElem(DL,i-1);
    if(NULL==p) return false;
    //为新插入的结点申请空间
    DLinkList s=(DLinkList)malloc(sizeof(DNode));
    s->data=e;
    s->next=p->next;
    p->next->prior=s;
    s->prior=p;
    p->next=s;
    return true;
}
//删除第i个结点
bool DListDelete(DLinkList DL,int i)
{
    DLinkList p=GetElem(DL,i-1);
    if(NULL==p) return false;
    DLinkList q;
    q=p->next;
    //删除的元素不存在
    if(q==NULL) return false;
    //断链
    p->next=q->next;
    if(q->next!=NULL){
        q->next->prior=p;
    }
    //释放对应结点的空间
    free(q);
    return true;
}
//链表打印
void PrintDList(DLinkList DL)
{
    DL=DL->next;
    while(DL!=NULL){
        printf("%3d",DL->data);
        DL=DL->next;
    }
    printf("
");
}

//双链表增删查
int main()
{
    DLinkList DL;
    DLinkList search;
    //Dlist_head_insert(DL);
    Dlist_tail_insert(DL);
    //3 4 5 6 7 9999
    PrintDList(DL);
    search=GetElem(DL,2);
    if(search!=NULL){
        printf("按序号查找成功
");
        printf("%3d
",search->data);
    }
    DListFrontInsert(DL,3,99);
    PrintDList(DL);
    DListDelete(DL,2);
    PrintDList(DL);
    system("pause");
}