複習下C 鏈表操作（雙向迴圈鏈表，尋找迴圈節點）

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雙向迴圈鏈表  和 單向迴圈鏈表 尋找迴圈節點 思路都是一樣。 快慢指標尋找法。 理論可參考

c 鏈表之 快慢指標 尋找迴圈節點

typedef struct Student_Double{    char name[10];    int  point;    struct Student_Double *preStu;    struct Student_Double *nextStu;} StudentDouble;StudentDouble *  CreateDoubleCircleLink_Table(){        int i = 0;    StudentDouble *head = NULL;    head=(StudentDouble *)malloc(sizeof(StudentDouble));    head->name[0]=‘\0‘;    head->point = 0;    head->nextStu = NULL;    head->preStu = NULL;        //迴圈節點    StudentDouble *cirleStu = NULL;    StudentDouble *temp = NULL;    StudentDouble *currentNode = head;    while (i<=9) {        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==3) {            cirleStu = currentNode;        }        i++;    }    //最後 合并迴圈節點    currentNode->nextStu=cirleStu;    return head;}//已知迴圈節點情況查詢迴圈 鏈表，驗證是否可用void SelectDoubleLinkTable(StudentDouble *student){    StudentDouble *next = student->nextStu;    int i = 0;    StudentDouble *circleStu = NULL;    while (next) {        if (circleStu!=NULL&&next->point == circleStu->point) {            printf("迴圈節點%d,結束迴圈\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->nextStu;    }}//未知情況查詢迴圈節點StudentDouble * SelectCircleNodeInDoubleLinkTable(StudentDouble *head){    //快慢指標查詢    StudentDouble *fast = head;    StudentDouble *slow = head;        while (fast) {        fast = fast->nextStu->nextStu;        slow = slow->nextStu;                if (fast==NULL) {//不是迴圈鏈表推出            break;        }        if (fast==slow) {//快慢指標相遇            break;        }    }    if (fast == NULL) {        printf("該鏈表 不是迴圈鏈表\n");        return NULL;    }        //尋找迴圈節點    fast = head;    while (fast!=slow) {        fast=fast->nextStu;        slow=slow->nextStu;    }    printf("=====找到迴圈鏈表迴圈節點為%d\n",fast->point);    return fast;}int main(void){    char sf[15];  //建立雙向迴圈鏈表    StudentDouble *head = NULL;    printf("建立雙向迴圈鏈表Y|N\n");    scanf("%s",sf);    if (strcmp(sf,"Y")==0) {        head = CreateDoubleCircleLink_Table();    }    printf("已知情況查詢迴圈鏈表Y|N \n");    scanf("%s",sf);    if (strcmp(sf,"Y")==0) {        SelectDoubleLinkTable(head);    }    printf("未知情況查詢迴圈鏈表Y|N \n");    scanf("%s",sf);    if (strcmp(sf,"Y")==0) {        SelectCircleNodeInDoubleLinkTable(head);    }    return 0;}

 

複習下C 鏈表操作（雙向迴圈鏈表，尋找迴圈節點）