6-1 在一个数组中实现两个堆栈 （20 分)

本题要求在一个数组中实现两个堆栈。

函数接口定义：
Stack CreateStack( int MaxSize );
bool Push( Stack S, ElementType X, int Tag );
ElementType Pop( Stack S, int Tag );
其中Tag是堆栈编号，取1或2；MaxSize堆栈数组的规模；Stack结构定义如下：

typedef int Position;
struct SNode {
ElementType *Data;
Position Top1, Top2;
int MaxSize;
};
typedef struct SNode *Stack;
注意：如果堆栈已满，Push函数必须输出“Stack Full”并且返回false；如果某堆栈是空的，则Pop函数必须输出“Stack Tag Empty”（其中Tag是该堆栈的编号），并且返回ERROR。

裁判测试程序样例：
#include <stdio.h>
#include <stdlib.h>

#define ERROR 1e8
typedef int ElementType;
typedef enum { push, pop, end } Operation;
typedef enum { false, true } bool;
typedef int Position;
struct SNode {
ElementType *Data;
Position Top1, Top2;
int MaxSize;
};
typedef struct SNode *Stack;

Stack CreateStack( int MaxSize );
bool Push( Stack S, ElementType X, int Tag );
ElementType Pop( Stack S, int Tag );

Operation GetOp(); /* details omitted /
void PrintStack( Stack S, int Tag ); / details omitted */

int main()
{
int N, Tag, X;
Stack S;
int done = 0;

scanf("%d", &N);
S = CreateStack(N);
while ( !done ) {
    switch( GetOp() ) {
    case push: 
        scanf("%d %d", &Tag, &X);
        if (!Push(S, X, Tag)) printf("Stack %d is Full!\n", Tag);
        break;
    case pop:
        scanf("%d", &Tag);
        X = Pop(S, Tag);
        if ( X==ERROR ) printf("Stack %d is Empty!\n", Tag);
        break;
    case end:
        PrintStack(S, 1);
        PrintStack(S, 2);
        done = 1;
        break;
    }
}
return 0;

}

/* 你的代码将被嵌在这里 */
输入样例：
5
Push 1 1
Pop 2
Push 2 11
Push 1 2
Push 2 12
Pop 1
Push 2 13
Push 2 14
Push 1 3
Pop 2
End
输出样例：
Stack 2 Empty
Stack 2 is Empty!
Stack Full
Stack 1 is Full!
Pop from Stack 1: 1
Pop from Stack 2: 13 12 11

代码如下：

Stack CreateStack( int MaxSize )
{
    struct SNode *S=NULL;
    S=(struct SNode *)malloc(sizeof(struct SNode));
    S->Data=(int *)malloc(MaxSize*sizeof(int));
    S->Top1=-1;
    S->Top2=MaxSize;
    S->MaxSize=MaxSize;
    return S;
}
bool Push( Stack S, ElementType X, int Tag )
{
    if(S->Top2-S->Top1==1)
    {
        printf("Stack Full\n");
        return false;
    }
    else
    {
        if(Tag==1) S->Data[++(S->Top1)]=X;
        else if(Tag==2) S->Data[--(S->Top2)]=X;
        return true;
    }
}
ElementType Pop( Stack S, int Tag )
{
    if(Tag==1)
    {
        if(S->Top1==-1)
        {
            printf("Stack %d Empty\n",Tag);
            return ERROR;
        }
        else return S->Data[(S->Top1)--];
    }
    else if(Tag==2)
    {
        if(S->Top2==S->MaxSize)
        {
            printf("Stack %d Empty\n",Tag);
            return ERROR;
        }
        else 
        {
            return S->Data[(S->Top2)++];
        }
    }
}