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Definition of queue
Queue: A first-in, first-out linear list A
queue is a linear list that only inserts at the end of the queue and deletes at the head of the queue
- Queue head (front): the head end of the linear table, you can delete the end
- Rear: the rear end of the linear table, which can be inserted into the end
Since there is a false overflow phenomenon in this queue, a circular linked list is introduced to solve the false overflow imagination
What is false overflow can refer to this article
circular queue
Two ways to distinguish whether a circular queue is full or empty
- Another flag is set to distinguish whether the queue is full or empty
- Use one less element space
Condition for empty team: Q.front == Q.rear Condition
for full team: (Q.rear+1)%MAXSIZE == Q.front
We use the second way to achieve
Basic Operations of Circular Queues
#include <iostream>
#define OK 1
#define ERROR 0
#define OVERFLOW -2
#define MAXSIZE 10
using namespace std;
typedef int Status;
typedef int QElemType;
typedef struct {
QElemType *base;//存储空间的基地址
int front;//头指针
int rear;//尾指针
}SqQueue;
/*初始化队列
1、为队列分配最大容量为MAXSIZE的数组空间,base指向数组空间的首地址
2、头指针和尾指针置为0,表示队列为空
*/
Status InitQueue(SqQueue &Q){
Q.base = new QElemType[MAXSIZE];
if (!Q.base) exit(OVERFLOW);//存储空间分配失败
Q.front = Q.rear = 0;//头尾指针置零
return OK;
}
/*队列的长度(队列中元素的个数)*/
int QueueLength(SqQueue Q){
return (Q.rear-Q.front+MAXSIZE)%MAXSIZE;
}
/*循环队列入队
1、判断队列是否已满,若满则返回ERROR
2、将新元素插入到队尾
3、队尾指针加1
*/
Status EnQueue(SqQueue &Q,QElemType e){
if ((Q.rear+1)%MAXSIZE == Q.front) //(循环)队列满了
return ERROR;
Q.base[Q.rear] = e;//在队尾插入元素
Q.rear = (Q.rear+1)%MAXSIZE;//队尾指针加1
return OK;
}
/*循环队列出队
1、判断队列是否为空,若空则返回ERROR
2、保存队头元素
3、队头指针加1
*/
Status DeQueue(SqQueue &Q,QElemType &e){
if (Q.front == Q.rear)//对空
return ERROR;
e = Q.base[Q.front];
Q.front = (Q.front+1)%MAXSIZE;//对头指针加1
return OK;
}
/*取循环队列的队头元素*/
QElemType GetHead(SqQueue Q){
if (Q.front != Q.rear)
return Q.base[Q.front];
}
int main(){
SqQueue Q;
InitQueue(Q);//初始化循环队列
EnQueue(Q,1);//循环队列入队
EnQueue(Q,2);
EnQueue(Q,3);
int length = QueueLength(Q);
cout<<length<<endl;
cout<<GetHead(Q)<<endl;
int a,b,c;
DeQueue(Q,a);//循环队列出队
DeQueue(Q,b);
DeQueue(Q,c);
cout<<a<<b<<c<<endl;
return 0;
}
chain team
A chain queue refers to a queue implemented with a chain storage structure. Usually the chain team is represented by a singly linked list. A chain team obviously needs two pointers to the head and tail of the team to be uniquely determined.
The basic operation of the chain team
#include <iostream>
#define OK 1
#define ERROR 0
#define OVERFLOW -2
#define MAXSIZE 10;
using namespace std;
typedef int Status;
typedef int QElemType;
typedef struct QNode{
QElemType data;
struct QNode *next;
}QNode,*QueuePtr;
typedef struct{
QueuePtr front;//头指针
QueuePtr rear;//尾指针
}LinkQueue;
/*链对的初始化
1、生成新结点作为头结点,队头和队尾指针都指向此结点
2、头节点的指针域置空
*/
Status InitQueue(LinkQueue &Q){
Q.front = Q.rear = new QNode;
Q.front->next = NULL;
return OK;
}
/*链队入队
1、为入队元素分配结点空间，用指针p指向
2、将新结点的数据与置为e
3、将新结点插入到队尾
4、修改队尾指针指向p
*/
Status EnQueue(LinkQueue &Q,QElemType e){
QueuePtr p = new QNode;
p->data = e;
p->next = NULL;
Q.rear->next = p;//修改尾指针
Q.rear = p;
return OK;
}
/*链队出队
1、判断队列是否为空,若空则返回ERROR
2、临时保存队头的元素空间,已备释放
3、修改队头指针指向下一个结点
4、判断出队元素是否为最后一个元素,若是则将队尾指针指向头结点
5、释放原队头元素的空间
*/
Status DeQueue(LinkQueue &Q,QElemType &e){
if (Q.rear == Q.front) //链队为空
return ERROR;
QueuePtr p = Q.front->next;
e = p->data;
Q.front->next = p->next;//修好头指针
if (Q.rear == p) //删除最后一个元素
Q.rear = Q.front;
delete p;
return OK;
}
/*取链队的队头元素*/
QElemType GetHead(LinkQueue Q){
if (Q.front != Q.rear)
return Q.front->next->data;
}
int main(){
LinkQueue Q;
InitQueue(Q);
EnQueue(Q,3);
EnQueue(Q,2);
EnQueue(Q,1);
int a,b,c;
DeQueue(Q,a);
DeQueue(Q,b);
DeQueue(Q,c);
cout<<a<<b<<c<<endl;
return 0;
}