已知p指向双向循环链表中的一个结点，其结点结构为data、prior、next三个域，写出算法change(p)，交换p所指向的结点和它的前缀结点的顺序。

#include<assert.h>
typedef struct SLnode
{int data;struct SLnode* prior;struct SLnode* next;
}SLnode,*SLnodelist;
//创建结点
SLnode* createhead(int data)
{SLnode* newnode = (SLnode*)malloc(sizeof(SLnode));newnode->data = data;newnode->next = newnode->prior = newnode;return newnode;
}
//初始化哨兵位
SLnode* ListInit()
{SLnode* newnode = createhead(0);
}
//尾插
void ListPushBank(SLnode* plist, int x)
{assert(plist);SLnode* ret = plist->prior;SLnode* newnode = createhead(x);ret->next = newnode;newnode->next = plist;newnode->prior = ret;plist->prior = newnode;
}
void printlist(SLnode* plist)
{SLnode* ret = plist->next;while (ret != plist){printf("%d->", ret->data);ret = ret->next;}printf("NULL\n");
}
void change(SLnodelist p)
{SLnodelist q;q = p->prior;q->prior->next = p;p->prior = q->prior;q->next = p->next;p->next->prior = q;q->prior = p;p->next = q;}
int main()
{int n, num;SLnode* plist = ListInit();printf("请输入链表的长度\n");scanf("%d", &n);printf("请输入元素\n");for (int i = 0; i < n; i++){scanf("%d", &num);ListPushBank(plist,num);}printf("双链表的元素如下\n");printlist(plist);printf("请输入你要交换的的结点的值\n");SLnodelist q = (SLnodelist)malloc(sizeof(SLnode));scanf("%d", &q->data);SLnodelist p;p = plist->next;while (p != plist){if (p->data == q->data){change(p);break;}else{p = p->next;}}printf("交换后\n");printlist(plist);return 0;
}