typedef struct Student_Double

{

    char name[];

    int  point;

    struct Student_Double *preStu;

    struct Student_Double *nextStu;

} StudentDouble;

StudentDouble *  CreateDoubleCircleLink_Table(){

    int i = ;

    StudentDouble *head = NULL;

    head=(StudentDouble *)malloc(sizeof(StudentDouble));

    head->name[]='\0';

    head->point = ;

    head->nextStu = NULL;

    head->preStu = NULL;

    //循环节点

    StudentDouble *cirleStu = NULL;

    StudentDouble *temp = NULL;

    StudentDouble *currentNode = head;

    while (i<=) {

        temp = (StudentDouble *)malloc(sizeof(StudentDouble));

        strncpy(temp->name,"Node",sizeof(temp->name));

        temp->point = i;

        temp->nextStu = NULL;

        temp->preStu = currentNode;

        currentNode->nextStu = temp;

        currentNode = temp;

        if (i==) {

            cirleStu = currentNode;

        }

        i++;

    }

    //最后 合并循环节点

    currentNode->nextStu=cirleStu;

    return head;

}

//已知循环节点情况查询循环 链表，验证是否可用

void SelectDoubleLinkTable(StudentDouble *student){

    StudentDouble *next = student->nextStu;

    int i = ;

    StudentDouble *circleStu = NULL;

    while (next) {

        if (circleStu!=NULL&&next->point == circleStu->point) {

            printf("循环节点%d,结束循环\n",next->point);

            break;

        }

        if (i==) {

            circleStu = next;

        }

        printf("index %d; studentName is %s;  point is %d\n",i,next->name,next->point);

        i++;

        next = next->nextStu;

    }

}

//未知情况查询循环节点

StudentDouble * SelectCircleNodeInDoubleLinkTable(StudentDouble *head){

    //快慢指针查询

    StudentDouble *fast = head;

    StudentDouble *slow = head;

    while (fast) {

        fast = fast->nextStu->nextStu;

        slow = slow->nextStu;

        if (fast==NULL) {//不是循环链表推出

            break;

        }

        if (fast==slow) {//快慢指针相遇

            break;

        }

    }

    if (fast == NULL) {

        printf("该链表 不是循环链表\n");

        return NULL;

    }

    //查找循环节点

    fast = head;

    while (fast!=slow) {

        fast=fast->nextStu;

        slow=slow->nextStu;

    }

    printf("=====找到循环链表循环节点为%d\n",fast->point);

    return fast;

}

int main(void){

    char sf[];

  //创建双向循环链表

    StudentDouble *head = NULL;

    printf("创建双向循环链表Y|N\n");

    scanf("%s",sf);

    if (strcmp(sf,"Y")==) {

        head = CreateDoubleCircleLink_Table();

    }

    printf("已知情况查询循环链表Y|N \n");

    scanf("%s",sf);

    if (strcmp(sf,"Y")==) {

        SelectDoubleLinkTable(head);

    }

    printf("未知情况查询循环链表Y|N \n");

    scanf("%s",sf);

    if (strcmp(sf,"Y")==) {

        SelectCircleNodeInDoubleLinkTable(head);

    }

    return ;

}