双端队列（deque，即double-ended queue的缩写）是一种具有队列和栈性质的数据结构，即可以（也只能）在线性表的两端进行插入和删除。若以顺序存储方式实现双端队列，请编写例程实现下列操作：

  • Push(X,D)：将元素X插入到双端队列D的头；
  • Pop(D)：删除双端队列D的头元素，并返回；
  • Inject(X,D)：将元素X插入到双端队列D的尾部；
  • Eject(D)：删除双端队列D的尾部元素，并返回。

函数接口定义：

bool Push( ElementType X, Deque D );
ElementType Pop( Deque D );
bool Inject( ElementType X, Deque D );
ElementType Eject( Deque D );

其中Deque结构定义如下：

typedef int Position;
typedef struct QNode *PtrToQNode;
struct QNode {
    ElementType *Data;      /* 存储元素的数组   */
    Position Front, Rear;   /* 队列的头、尾指针 */
    int MaxSize;            /* 队列最大容量     */
};
typedef PtrToQNode Deque;

注意：Push和Inject应该在正常执行完操作后返回true，或者在出现非正常情况时返回false。当Front和Rear相等时队列为空，Pop和Eject必须返回由裁判程序定义的ERROR。

裁判测试程序样例：

#include <stdio.h>
#include <stdlib.h>

#define ERROR -1
typedef int ElementType;
typedef enum { push, pop, inject, eject, end } Operation;
typedef enum { false, true } bool;
typedef int Position;
typedef struct QNode *PtrToQNode;
struct QNode {
    ElementType *Data;      /* 存储元素的数组   */
    Position Front, Rear;   /* 队列的头、尾指针 */
    int MaxSize;            /* 队列最大容量     */
};
typedef PtrToQNode Deque; 

Deque CreateDeque( int MaxSize )
{   /* 注意：为区分空队列和满队列，需要多开辟一个空间 */
    Deque D = (Deque)malloc(sizeof(struct QNode));
    MaxSize++;
    D->Data = (ElementType *)malloc(MaxSize * sizeof(ElementType));
    D->Front = D->Rear = 0;
    D->MaxSize = MaxSize;
    return D;
}

bool Push( ElementType X, Deque D );
ElementType Pop( Deque D );
bool Inject( ElementType X, Deque D );
ElementType Eject( Deque D );

Operation GetOp();          /* 裁判实现，细节不表 */
void PrintDeque( Deque D ); /* 裁判实现，细节不表 */

int main()
{
    ElementType X;
    Deque D;
    int N, done = 0;

    scanf("%d", &N);
    D = CreateDeque(N);
    while (!done) {
        switch(GetOp()) {
        case push: 
            scanf("%d", &X);
            if (!Push(X, D)) printf("Deque is Full!\n");
            break;
        case pop:
            X = Pop(D);
            if ( X==ERROR ) printf("Deque is Empty!\n");
            else printf("%d is out\n", X);
            break;
        case inject: 
            scanf("%d", &X);
            if (!Inject(X, D)) printf("Deque is Full!\n");
            break;
        case eject:
            X = Eject(D);
            if ( X==ERROR ) printf("Deque is Empty!\n");
            else printf("%d is out\n", X);
            break;
        case end:
            PrintDeque(D);
            done = 1;
            break;
        }
    }
    return 0;
}

/* 你的代码将被嵌在这里 */

输入样例：

3
Pop
Inject 1
Pop
Eject
Push 2
Push 3
Eject
Inject 4
Inject 5
Inject 6
Push 7
Pop
End

输出样例：

Deque is Empty!
1 is out
Deque is Empty!
2 is out
Deque is Full!
Deque is Full!
3 is out
Inside Deque: 4 5


样例没啥用，编译器编译过不了所以就干写了四个函数，要注意尾指针需要减一。

代码：

bool Push( ElementType X, Deque D )
{
    if((D->Rear - D->Front + D->MaxSize)%D->MaxSize != D->MaxSize - 1)
    {
        D->Front = (D->Front - 1 + D->MaxSize)%D->MaxSize;
        D->Data[D->Front] = X;
    }
    else return false;
    return true;
}
ElementType Pop( Deque D )
{
    if(D->Rear != D->Front)
    {
        ElementType a = D->Data[D->Front];
        D->Front = (D->Front + 1)%D->MaxSize;
        return a;
    }
    else return ERROR;
}
bool Inject( ElementType X, Deque D )
{
    if((D->Rear - D->Front + D->MaxSize)%D->MaxSize != D->MaxSize - 1)
    {
        D->Data[D->Rear] = X;
        D->Rear = (D->Rear + 1)%D->MaxSize;
    }
    else return false;
    return true;
}
ElementType Eject( Deque D )
{
    if(D->Rear != D->Front)
    {
        D->Rear = (D->Rear - 1 + D->MaxSize)%D->MaxSize;
        ElementType a = D->Data[D->Rear];
        return a;
    }
    else return ERROR;
}