共享栈

利用栈底为止相对不变的特性，可让两个顺序栈共享一个一维数组空间，将两个栈的栈底分别设置在共享空间的两端，两个栈顶向共享空间的中间延伸。

//
//  sharestack.c
//  Ccode
//
//  Created by XX on 2020/4/8.
//  Copyright © 2020 XX. All rights reserved.
//

#include "sharestack.h"
#include <stdlib.h>
#define MAX 

#define MaxSize 5//定义栈中元素的最大个数
typedef int ElemType;
typedef struct shareStack {
    ElemType data[MaxSize];
    int top0;
    int top1;
}shareStack, *pshare;


pshare CreateShare() {
    pshare p = (shareStack *)malloc(sizeof(shareStack));
    p->top0 = -1;
    p->top1 = MaxSize;
    return p;
}

//判空
int EmptyShare(pshare p) {
    if (p->top0 == -1 && p->top1 == MaxSize) {
        return 0;
    }
    return -1;
}

//入栈
int PushShare(pshare p, ElemType data, int stackNum) {
    if (p == NULL) {
        exit(-1);
    }
    if (p->top0 + 1 == p->top1) {
        printf("栈满...\n");
        return 0;
    }
    switch (stackNum) {
        case 0:
            p->top0 ++;
            p->data[p->top0] = data;
            return 0;
        case 1:
            p->top1 --;
            p->data[p->top1] = data;
            return 0;
            
        default:
            return -1;
    }
}

//出栈
int PopShare(pshare p, int stackNum) {
    int data;
    if (p == NULL) {
        exit(-1);
    }
    if (p->top0 == -1 && p->top1 == MaxSize) {
        return -1;
    }
    switch (stackNum) {
        case 0:
            data = p->data[p->top0];
            p->top0 --;
            return data;
        case 1:
            data = p->data[p->top1];
            p->top1 ++;
            return data;
        default:
            return -1;
    }
}


void testshare() {
    int data;
    shareStack s;
    pshare top = &s;
    top = CreateShare();
    PushShare(top, 23, 0);
    PushShare(top, 23, 0);
    PushShare(top, 78, 0);
    PushShare(top, 23, 1);
    PushShare(top, 45, 1);
    PushShare(top, 34, 0);
    data = PopShare(top, 0);
    printf("%d\n", data);
}