快慢指针查找未知长度单链表中间值

快慢指针查找位置长度的单链表的中间值。。。。

根据步长不同，也可以用来查找三分之一处，四分之一处。。。。。。

typedef struct List
{
    int data;
    struct List * next;
}List;

void list_init(List *head, const int len);
void search(List *head);
void list_print(List *head);
void list_des(List *head);

int main()
{
    int len = 0;
    List head = {0, NULL};
    
    printf("输入长度：");
    scanf("%d", &len);
    
    list_init(&head, len);
    list_print(&head);
    search(&head);
    list_des(&head);
    return 0;
 } 

void list_init(List *head, const int len)
{
    int i = 0;
    List *p = head;
    
    for(i=0; i<len; i++)
    {
        p->next = (List *)malloc(sizeof(List));
        p = p->next;
        p->data = i+1;
        p->next = NULL;
    }
}

void search(List *head)
{
    List *search = head;
    List *middle = head;
    
    while(search)
    {
        if(search->next) {
            search = search->next->next;
        }else {
            search = search->next;
        }
        
        middle = middle->next;
    }
    
    printf("middle data: %d
", middle->data);
}

void list_print(List *head)
{
    List *p = head;
    
    while(p->next)
    {
        p = p->next;
        printf("%d ", p->data);
    }
    printf("
");
}

void list_des(List *head)
{
    List *p = head->next;
    List *q = NULL;
    
    while(p)
    {
        q = p->next;
        free(p);
        
        p = q;
        
    }
    
    head->next = NULL;
}