6-1 Deque

6-1 Deque （25 分）

A "deque" is a data structure consisting of a list of items, on which the following operations are possible:

• Push(X,D): Insert item X on the front end of deque D.
• Pop(D): Remove the front item from deque D and return it.
• Inject(X,D): Insert item X on the rear end of deque D.
• Eject(D): Remove the rear item from deque D and return it. Write routines to support the deque that take O(1) time per operation.

Format of functions:

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

where Deque is defined as the following:

typedef struct Node *PtrToNode;
struct Node {
    ElementType Element;
    PtrToNode Next, Last;
};
typedef struct DequeRecord *Deque;
struct DequeRecord {
    PtrToNode Front, Rear;
};

Here the deque is implemented by a doubly linked list with a header. Front and Rear point to the two ends of the deque respectively. Front always points to the header. The deque is empty when Front and Rear both point to the same dummy header. Note: Push and Inject are supposed to return 1 if the operations can be done successfully, or 0 if fail. If the deque is empty, Pop and Eject must return ERROR which is defined by the judge program.

Sample program of judge:

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

#define ElementType int
#define ERROR 1e5
typedef enum { push, pop, inject, eject, end } Operation;

typedef struct Node *PtrToNode;
struct Node {
    ElementType Element;
    PtrToNode Next, Last;
};
typedef struct DequeRecord *Deque;
struct DequeRecord {
    PtrToNode Front, Rear;
};
Deque CreateDeque();
int Push( ElementType X, Deque D );
ElementType Pop( Deque D );
int Inject( ElementType X, Deque D );
ElementType Eject( Deque D );

Operation GetOp();          /* details omitted */
void PrintDeque( Deque D ); /* details omitted */

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

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

/* Your function will be put here */

Sample Input:

Pop
Inject 1
Pop
Eject
Push 1
Push 2
Eject
Inject 3
End

Sample Output:

Deque is Empty!
Deque is Empty!
Inside Deque: 2 3

Deque CreateDeque() {
    PtrToNode p = (PtrToNode)malloc(sizeof(struct Node));
    Deque d = (Deque)malloc(sizeof(struct DequeRecord));
    p->Last = p->Next = NULL;
    d->Front = d->Rear = p;
    return d;
}
int Push(ElementType X, Deque D) {     //注意！  首节点不存元素！！！ 插入在首节点后面
    if (D == NULL) return 0;
    D->Front->Element = X;     
    PtrToNode p = (PtrToNode)malloc(sizeof(struct Node));
    D->Front->Last = p;
    p->Next = D->Front;
    D->Front = p;
    return 1;
}
ElementType Pop(Deque D) {   //注意！  开始删除删头结点后面的结点
    if (D->Front == D->Rear || D == NULL) return ERROR;
    PtrToNode t = D->Front->Next;
    ElementType e = t->Element;
    if (t == D->Rear) {
        D->Rear=D->Front;
    }
    else {
    D->Front->Next = t->Next;
    t->Next->Last = D->Front;
    }
    free(t);
    return e;
}
int Inject(ElementType X, Deque D) {   //注意！  尾节点要存元素！！！
    if (D == NULL) return 0;
    PtrToNode p = (PtrToNode)malloc(sizeof(struct Node));
    p->Element = X;
    D->Rear->Next = p;
    p->Last = D->Rear;
    D->Rear = p;
    return 1;
}
ElementType Eject(Deque D) {    //注意！  后面删除删最后一个 
    if (D->Front == D->Rear||D==NULL) return ERROR;
    PtrToNode p = D->Rear;
    ElementType e = D->Rear->Element;
    D->Rear = D->Rear->Last;
    free(p);
    return e;
}