2-25练习题

6.假设循环队列用数组实现,其定义如下:
#define SEQLEN 32
int seqn [ SEQLEN ];
/*用于存放队列数据的数组*/
int head;/*数组下标索引，指向队列头部，若队列不空，指向队列头元素*/
int tail;/*数组下标索引，指向队列尾部，若队列不空，指向队列空元素*/
队列示例:
循环队列中保存了1、2,3三个数据的状态。
seqn
head=1
tail=4
(1)假如队列未满，现有变量 data 需要入队，请写出表达式;
seqn[tail] = data;
tail = (tail + 1) % SEQLEN;

(2)假如队列未空，现在需要从队列取一个元素并赋值给变量data，请写出表达式;
data = seqn[head];
head = (head + 1) % SEQLEN;

(3)请写出队列为空的判断条件:
head == tail

(4)请写出队列满的判断条件:
(head + 1) % SEQLEN == tail

(5)请写出清空队列的表达式:
head = 0;
tail = 0;

(6)请写出计算队列中元素个数的表达式:
(head <= tail) ? (tail - head) : (SEQLEN - head + tail)

(7)队列最多可以存放几个元素:
循环队列最多可以存放的元素个数为 SEQLEN - 1，因为需要浪费一个位置来区分队列为空和队列为满的状态。
所以最多可以存放31个元素。

6, 补下面队列代码
struct list_head {
   struct list_head *next, *prev;
};
/**
* used to add new element into list.
* @new: specify the new element.
* @prev: specify the previous element.
* @next: specify the next element.
* 插入到 prev 和 next 中间
*/
static inline void _list_add(struct list_head * new,
struct list_head * prev,
struct list_head *next)
}

   new=(struct list_head*)malloc(sizeof(struct list_head));
   if(NULL = new）
   {
       printf("创建新节点失败\n");
       return;
   }
   new->next = NULL;
   new->prev = NULL;
   new->prev=new->prev->next;
   new->prev->next = new;


/**
* used to maintain link status when delete an element.
*@prev: specify the previous element.
*@next: specify the next element.
* 删除 prev 和 next 中间那个
*/
static inline void __list_del(struct list_head *prev, struct list_head *next)
{
   struct list_head* p;
   p=prev->next;
   prev->next = prev->next->next;
   free(p);
   p=NULL;

}
/**
* used to add element into the tall of list.
* @new: specify the new element.
* @head: specify the head element.
* 插入到队尾
* /
static inline void list_add_tail(struct list_head *new, struct list_head *head)
{

   new=(struct list_head*)malloc(sizeof(struct list_head));
   if(NULL = new)
   {
       printf("申请新节点失败\n");
       return;
   }
   p=head;
   while(p->next!=NULL)
   {
       p=p->next;
   }
   p->next = new->next;
   p->next = new;
   new->prev = p;
   new->next=NULL;

}
/**
* used to remove element.
* @entry: specify the element which want to be deleted.
* 删掉
*/
static inline void list_del(struct list_head *entry)
{
   struct list_head* p;
   if(entry->next!=NULL)
   {
       entry->prev->next = entry->next;
       entry->next->prev = entry->prev;
       free(entry);
       entry=NULL;
   }
   else
   {
       entry->prev->next = NULL;
       free(entry);
       entry=NULL;
   }
}
/**
* used to check list is empty or not.
* @head: specify the head element.
* 判断是否为空
*/
static inline int list_empty(const struct list_head *head)
{
   return head->next == head->prev;
}