复习下C 链表操作（单向循环链表、查找循环节点）

//创建 循环链表
Student * CreateCircleLink_Table(void){
int i = 0;
Student *head = NULL;
head = (Student *)malloc(sizeof(Student));
head->name[0]='\0';
head->point = 0;
head->stu = NULL;
//循环节点
Student *circleStu = NULL;
Student *temp = NULL;
Student *currentNode = head;
while (i<=9) {

temp = (Student *)malloc(sizeof(Student));
strncpy(temp->name,"Node",sizeof(temp->name));
temp->point = i;
temp->stu = NULL;

currentNode->stu = temp;
currentNode = temp;

//循环节点
if (i==3) {
circleStu = currentNode;
}

i++;
}

//最后 合并循环节点
currentNode->stu = circleStu;

return head;
}

//已知循环节点 查询 主要为了验证循环链表是否可用
void SelectCircleLinkTable(Student *student){
Student *next = student->stu;
int i = 0;
Student *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==3) {
circleStu = next;
}
printf("index %d; studentName is %s;  point is %d\n",i,next->name,next->point);
i++;
next = next->stu;
}
}

//查找循环链表中循环节点
Student * SelectCircleNodeInLinkTable(Student *student) {
Student *fast = student;
Student *slow = student;

Student *circleStu = NULL;
while (fast->stu) {
fast = fast->stu->stu;//快指针节点 为慢指针节点的2倍
slow = slow->stu;

if (fast==NULL) { //不存在循环节点
return NULL;
}
if (fast == slow) {//快慢指针相遇。找到循环节点
circleStu = fast;
break;
}

}

if (fast==NULL) { //不存在循环节点
return NULL;
}
printf("相遇节点为==%d\n",circleStu->point);
fast=student;
while (fast!=slow) {
slow=slow->stu;
fast=fast->stu;
}
return fast;
}

int main(void){
char sf[15];

//    /**
//     *  创建单向链表
//     */
//    int num;
//    printf ("请输入学生人数\n");
//    scanf("%d",&num);
//    Student *link_stu = CreateLink_Table(num);
//
//
//    /**
//     *  单向链表插入节点
//     */
//    printf ("请插入节点内容 在 已存在节点名字的后面，如 已存在节点名字|待插入名字|待插入分数 \n");
//    scanf("%s",sf);
//
//    link_stu = insertStudentLinkTable(link_stu,sf);
//
//    /**
//     *  反转单向链表
//     */
//    printf("反转链表Y|N \n");
//    scanf("%s",sf);
//    if (strcmp(sf,"Y")==0) {
//       Student *newLt= ReversionStudentLinkTable(link_stu);
//        //查询
//        selectStudent(newLt);
//    }

/**
*  创建循环链表
*/
Student *student = NULL;
printf("开始创建循环链表Y|N \n");
scanf("%s",sf);
if (strcmp(sf,"Y")==0) {
student =  CreateCircleLink_Table();
}

printf("已知情况查询循环链表Y|N \n");
scanf("%s",sf);
if (strcmp(sf,"Y")==0) {
SelectCircleLinkTable(student);
}

printf("未知情况查询循环链表Y|N \n");
scanf("%s",sf);
if (strcmp(sf,"Y")==0) {
Student *circleStu = SelectCircleNodeInLinkTable(student);
printf("=====循环节点==%d\n",circleStu->point);
}

return 0;
}