顺序队列

       顺序队列是一种先进先出的线性表，简称FIFO。允许插入的一端称为队尾，允许删除的一端称为队头。因为其入队和出队操作均是（front/rear）指针向后移动，以进行结点的链接和删除，这就造成其使用空间不断向出队的那一边偏移，当出队入队次数频繁时，尾指针移动到我们可以进行队列操作的范围之外去了，则会产生假溢出。

（当使用动态链表创建顺序队列，其向后继续不断的申请内存空间，即使前面出队操作释放掉了前面的空间，但是指针依旧会向后进行移动，直到达到系统预留给程序的内存上界被强行终止）。

循环队列

        循环队列就是为了解决顺序队列的“假溢出”问题，即将顺序队列臆造为一个环状的空间。循环队列中指针和队列元素之间的关系不变，我们只需要利用模运算就可以很容易实现指针的循环移动。

        但是循环队列中存在一个问题，在循环队列中只凭头指针front等于尾指针rear无法判别队列空间是“空”还是“满”，可有两种处理方法：

     （一）设置队列元素个数成员，以区别队列是“空”还是“满”；

     （二）front指针表示为虚拟头指针，即不指向元素，队列的实际元素数量要比队列空间maxsize少一个，如下图所示，队列总长度为8，实际元素个数为7个，还有一个被front指针使用。

（一）设置队列元素个数成员，以区别队列是“空”还是“满”；

// vector实现循环队列#include<iostream>
#include<vector>
using namespace std;class cirQueue
{
public:int maxsize;int front;int rear;int count;vector<int> data;public:cirQueue(){this->count = 0;this->maxsize = 8;this->front = 0;this->rear = 0;for(int i=0; i<maxsize; i++){this->data.push_back(0);}}cirQueue(int maxsize):count(0),maxsize(maxsize),front(0),rear(0){for(int i=0; i<maxsize; i++){this->data.push_back(0);} }void push_cirQueue(int data);void pop_cirQueue();void show_cirQueue();
};// 入队
void cirQueue::push_cirQueue(int val){//满了(rear的下一个元素是front），再继续就溢出 if( (this->rear+1)%maxsize == this->front ){cout<<"the cirQueue is full!"<<endl;}//从rear加入元素else{// 判断队列是否为空if(this->count == 0){this->data[this->rear] = val;}else{this->rear = (this->rear+1)%maxsize;this->data[this->rear] = val;    }this->count++;}
}// 出队
void cirQueue::pop_cirQueue(){//判断队列是否为空if(this->count == 0){cout<<"the cirQueue is empty!"<<endl;}//front出队else{this->data[this->front] = 0;this->front = (this->front+1)%maxsize;}this->count--;
}void cirQueue::show_cirQueue(){if(this->count == 0){cout<<"the cirQueue is empty!"<<endl;}else{int cur = this->front;cout<<this->data[cur]<<", ";while(cur != this->rear){cur = (cur+1)%maxsize;cout<<this->data[cur]<<", ";}cout<<endl;}
}int main()
{cirQueue myCirQueue(5);myCirQueue.show_cirQueue();cout<<"front:"<<myCirQueue.front<<" rear:"<<myCirQueue.rear<<endl;myCirQueue.push_cirQueue(1);myCirQueue.push_cirQueue(2);myCirQueue.push_cirQueue(3);myCirQueue.push_cirQueue(4);myCirQueue.push_cirQueue(5);myCirQueue.show_cirQueue();cout<<"front:"<<myCirQueue.front<<" rear:"<<myCirQueue.rear<<endl;myCirQueue.push_cirQueue(6);myCirQueue.show_cirQueue();myCirQueue.pop_cirQueue();myCirQueue.show_cirQueue();cout<<"front:"<<myCirQueue.front<<" rear:"<<myCirQueue.rear<<endl;return 0;
}

 

（二） front指针表示为虚拟头指针，即不指向元素，

// vector实现循环队列#include<iostream>
#include<vector>
using namespace std;class cirQueue
{
public:int maxsize;int front;int rear;int count;vector<int> data;public:cirQueue(){this->count = 0;this->maxsize = 8;this->front = 0;this->rear = 0;for(int i=0; i<maxsize; i++){this->data.push_back(0);}}cirQueue(int maxsize):count(0),maxsize(maxsize),front(0),rear(0){for(int i=0; i<maxsize; i++){this->data.push_back(0);} }void push_cirQueue(int data);void pop_cirQueue();void show_cirQueue();
};// 入队
void cirQueue::push_cirQueue(int val){//满了(rear的下一个元素是front），再继续就溢出 if( (this->rear+1)%maxsize == this->front ){cout<<"the cirQueue is full!"<<endl;}//从rear加入元素else{this->rear = (this->rear+1)%maxsize;this->data[this->rear] = val;this->count++;}
}// 出队
void cirQueue::pop_cirQueue(){//判断队列是否为空if(this->front == this->rear){cout<<"the cirQueue is empty!"<<endl;}//front出队else{this->data[this->front] = 0;this->front = (this->front+1)%maxsize;}this->count--;
}void cirQueue::show_cirQueue(){if(this->front == this->rear){cout<<"the cirQueue is empty!"<<endl;}else{int cur = this->front;while(cur != this->rear){cur = (cur+1)%maxsize;cout<<this->data[cur]<<", ";}cout<<endl;}
}int main()
{cirQueue myCirQueue(5);myCirQueue.show_cirQueue();cout<<"front:"<<myCirQueue.front<<" rear:"<<myCirQueue.rear<<endl;myCirQueue.push_cirQueue(1);myCirQueue.push_cirQueue(2);myCirQueue.push_cirQueue(3);myCirQueue.push_cirQueue(4);myCirQueue.push_cirQueue(5);myCirQueue.show_cirQueue();cout<<"front:"<<myCirQueue.front<<" rear:"<<myCirQueue.rear<<endl;myCirQueue.push_cirQueue(6);myCirQueue.show_cirQueue();myCirQueue.pop_cirQueue();myCirQueue.show_cirQueue();cout<<"front:"<<myCirQueue.front<<" rear:"<<myCirQueue.rear<<endl;return 0;
}