队列

1.队列实现的是一种先进进先出的策略，即被删除的是最先插入的元素（也称为FIFO，即先进先出）

2.基本成员函数：

back()返回最后一个元素

empty()如果队列空则返回真

front()返回第一个元素

pop()删除第一个元素

push()在末尾加入一个元素

size()返回队列中元素的个数

3.队列的实现

include<cassert>
#include<iostream>
using namespace std;
template<typename T>
class Queue
{
public:
    Queue(int maxsize = 10);
    Queue(const Queue<T>& rhs);
    Queue<T>& operator=(const Queue<T>& rhs);
    ~Queue();
public:
    bool empty() const;
    bool IsFull() const;
    int size() const;

    void push(const T& data);
    void pop();
    T& front();
    T   front() const;
    T& back();
    T   back() const;
private:
    T *array;
    int Front;//头部   当Front=rear时表示队列已满，当Front+1=rear时，表示队列已满
    int rear;//尾部
    int capacity;
};

template<typename T>
Queue<T>::Queue(int maxsize) :Front(0), rear(0),capacity(maxsize)
{
    array = new T[maxsize];
    assert(array != NULL);    //存储分配失败则退出;
}

template<typename T>
Queue<T>::Queue(const Queue<T>& rhs) :Front(rhs.Front), rear(rhs.rear),capacity(rhs.capacity)
{
    array = new T[capacity];
    for (int i = 0; i != (this->size()); i++)
        array[i] = rhs.array[i];
}

template<typename T>
Queue<T>& Queue<T>::operator=(const Queue<T>& rhs)
{
    if (this != &rhs)
    {
        delete[] array;
        capacity = rhs.capacity;
        Front = rhs.Front;
        rear = rhs.rear;
        array = new T[capacity];
        for (int i = 0; i != (this->size()); i++)
            array[i] = rhs.array[i];
    }
    return *this;
}
template<typename T>
Queue<T>::~Queue()
{
        delete[] array;
}

template<typename T>
bool Queue<T>::empty() const
{
    return Front == rear;      //此处为循环队列，当front==rear时为空。
}

template<typename T>
bool Queue<T>::IsFull() const
{
    return(rear + 1) % capacity == Front;   //当（rear+1）%capacity==front为满,因为为满时差一个元素，但是可能rear>front,也可能rear<front.
}

template<typename T>
int Queue<T>::size() const
{
    return (rear - Front + capacity) % capacity;
}

template<typename T>
void Queue<T>::push(const T& data)
{
    if (!IsFull())
    {
        array[rear] = data;
        rear = (rear + 1) % capacity;//这里是循环队列的实现
    }
    else                                                  //当队列满了之后可进行扩容
    {
        T *newarray=new T[ 2*capacity ];
        for (int i = 0; i != 2*capacity&&!this->empty(); i++)
        {
            newarray[i] =this-> front();
            this->pop();//将之前的队列全部复制过来
        }
        delete [ ] array;//再将之前的队列释放
        array = newarray;//将指针指向新的空间，从而达到扩容的效果
        Front = 0;
        array[rear] = data;
        rear =this->rear+1;
        capacity = 2*capacity;
    }
}

template<typename T>
void Queue<T>::pop()
{
    if (!empty())
    {
        //array[Front].~T();   //将队头元素析构掉
        Front = (Front + 1) % capacity;
    }
    else
        cout<<"empty queue!"<<endl;
}

template<typename T>
T& Queue<T>::front()
{
    if (empty())
        cerr << "Error, queue is empty!";
    return array[Front];
}
template<typename T>
T Queue<T>::front() const
{
    if (empty())
        cerr << "Error, queue is empty!";
    return array[Front];
}
template<typename T>
T& Queue<T>::back()
{
    if (empty())
        cerr << "Error, queue is empty!";
    return array[rear-1];                             //rear类似与尾后指针
}
template<typename T>
T Queue<T>::back() const
{
    if (empty())
        cerr << "Error, queue is empty!";
    return array[rear-1];
}