10.1-5

CLRS 10.1-5
栈的插入和删除操作都是在一端进行的，而队列的插入和删除却是在两头进行的。有一种双端队列(deque)，其两端都可以做插入和删除的操作。对于一个用数组构造的双端队列，请写出四个在两端进行插入和删除操作的过程，要求运行时间为O(1)。

 

#include <iostream>
usingnamespace std;

template <class T>
class Deque
{
public:
  void push_front(T t);
  void push_back(T t);
  T pop_front();
  T pop_back();
  Deque(int m);
  ~Deque();

 

private:
  T* arr;
  int max;
  int count;
  int head;
  int tail;
};

int main()
{
  Deque<int> d(3);
  d.push_front(0);
  d.push_back(2);
  d.push_front(4);

  cout<<d.pop_front()<<endl;
  d.push_back(3);
  cout<<d.pop_back()<<endl;
  return0;
}

template <class T>
void Deque<T>::push_front(T t)
{
  if(count == max)
  {
    cout<<"deque is full"<<endl;
    return;
  }
  //保证新插入的元素总在前面
  head = (head ==0) ? max -1 : head -1;
  arr[head] = t;
  count++;
}

template <class T>
void Deque<T>::push_back(T t)
{
  if(count == max)
  {
    cout<<"deque is full"<<endl;
    return;
  }
  //保证新插入的元素总在后面
  tail = (tail == max -1) ?0 : tail +1;
  arr[tail] = t;
  count++;
}

template <class T>
T Deque<T>::pop_front()
{
  if(count ==0)
  {
    cout<<"deque is empty"<<endl;
    return NULL;
  }
  int temp = head;
  head = (head == max -1) ?0 : head +1;
  count--;
  return arr[temp];
}

template <class T>
T Deque<T>::pop_back()
{
  if(count ==0)
  {
    cout<<"deque is empty"<<endl;
    return NULL;
  }
  int temp = tail;
  tail = (tail ==0) ? max -1 : tail -1;
  count--;
  return arr[temp];
}

template <class T>
Deque<T>::Deque(int m)
{
  max = m;
  count =0;
  head =0;
  tail = m -1;
  arr =new T[m];
}

template <class T>
Deque<T>::~Deque()
{
  delete[] arr;
}