4.双向链表复制——双向链表

设一带头结点的双向循环链表表示的线性表：L =（a1, a2, …… , an）
请写出一个时间复杂度为O(n)的算法，将L改造为：L =（a1, a2, ……, an-1, an, an-1, ……, a2, a1）

预设代码

/* PRESET CODE BEGIN - NEVER TOUCH CODE BELOW */

/*
设一带头结点的双向循环链表表示的线性表：
L =（a1, a2, …… , an）
请写出一个时间复杂度为O(n)的算法，将L改造为：
L =（a1, a2, ……, an-1, an, an-1, ……, a2, a1）
*/

#include 
#include  

typedef int ElemType;
typedef struct DuLNode {
    ElemType        data;      // 数据域
    struct DuLNode  *prior;	   // 指向前驱的指针域
    struct DuLNode  *next;	   // 指向后继的指针域
} DuLNode, * DuLinkList;

// 函数原型 
void out_next(DuLinkList);
void out_prior(DuLinkList);
void rcopy(DuLinkList);		//这是你要编写的函数 

// 函数定义 
void out_next(DuLinkList DHead)
{	DuLinkList p = DHead->next; 
	while ( p != DHead )
	{	printf("%d,", p->data);
		p = p->next;
	}
	printf("\n");
}
void out_prior(DuLinkList DHead)
{	DuLinkList p = DHead->prior; 
	while ( p != DHead )
	{	printf("%d,", p->data);
		p = p->prior;
	}
	printf("\n");
}

int main()
{	DuLinkList DHead, p;
	int num;
	
	DHead = (DuLNode*)malloc( sizeof(DuLNode));
	DHead->data = -1;
	DHead->prior = DHead->next = DHead;   	// 生成表头

	scanf("%d", &num);
	while ( num != -1 )
	{	p = (DuLNode*)malloc( sizeof(DuLNode));
		p->data = num;
		p->next = DHead->next;	// 1.链接p的next链 
		DHead->next = p;		// 2.链接DHead的next链
		p->next->prior = p;		// 3.链接p的next的prior链
		p->prior = DHead;		// 4.链接p的prior链
		scanf("%d", &num);
	}
	printf("Link  next:");	out_next( DHead );
	printf("Link prior:");	out_prior( DHead );
	rcopy( DHead );
	printf("NewL  next:");	out_next( DHead );
	printf("NewL prior:");	out_prior( DHead );
	return 0;
}
/**************************************
void rcopy(DuLinkList DHead)
{
    This function is wating for you.
}
***************************************/

/* PRESET CODE END - NEVER TOUCH CODE ABOVE */

测试用例
in:
1 2 3 4 5 -1
out:
Link next:5,4,3,2,1,↵
Link prior:1,2,3,4,5,↵
NewL next:5,4,3,2,1,2,3,4,5,↵
NewL prior:5,4,3,2,1,2,3,4,5,↵

void rcopy(DuLinkList head)
{
	DuLinkList s,p,q;
	p=head->next;
	q=head->next;
	while(p->next!=head)
		p=p->next;
	while(q->next->next!=head)
		q=q->next;
	if(q->data==-1)
		return ;
	while(q->data!=-1)
	{
		s=(DuLNode*)malloc(sizeof(DuLNode));
		s->data=q->data;
		s->next=head;
		head->prior=s;
		p->next=s;
		s->prior=p;
		q=q->prior;
		p=p->next;
	}
	s->next=head;
	head->prior=s;
}