共享栈

共享栈，即是两个栈使用同一段存储空间。

第一个栈从数组头开始存储，第二个栈从数组尾开始，两个栈向中间拓展。

当top1+1==top2或者top1==top2-1时，即staock overflow!.

与普通栈一样，共享栈出栈入栈的时间复杂度仍为O(1).

数据结构

typedef struct shareStack{
    int data[MAXSIZE];
    int top1;
    int top2;
}shareStack;

出栈操作

该数据，仅存的是非负数，因此如果想要存储更复杂的操作，可以在判断栈空时，换一种方式，即可。

int Pop(shareStack *ss,int flag){
    if(flag == 1){
        if(ss->top1 == -1)
            return -1;
        return ss->data[ss->top1--];
    }else if(flag == 2){
        if(ss->top2 == MAXSIZE)
            return -1;
        return ss->data[ss->top2++];
    }
    return -1;
}

入栈操作

int Push(shareStack *ss,int num,int flag){
    if(ss->top1+1 == ss->top2)
        return 0;
    if(flag == 1){
        ss->data[++ss->top1] = num;
        return 1;
    }else if( flag == 2){
        ss->data[--ss->top2] = num;
        return 1;
    }
    return 0;
}

示例代码

#include <stdio.h>
#include <stdlib.h>
#define MAXSIZE 20

typedef struct shareStack{
    int data[MAXSIZE];
    int top1;
    int top2;
}shareStack;

void createStack(shareStack * ss,int n,int m);
void showStack(shareStack *ss);
int Push(shareStack *ss,int num,int flag);
int Pop(shareStack *ss,int flag);

int main()
{
    shareStack * ss = (shareStack *)malloc(sizeof(shareStack));

    createStack(ss,3,4);
    showStack(ss);

    if(Push(ss,6,1))
        showStack(ss);

    if(Push(ss,4,2))
        showStack(ss);

    int n;
    n=Pop(ss,1);
    if(n>=0)
        printf("the pop num is:%d
",n);
    n=Pop(ss,2);
    if(n>=0)
        printf("the pop num is:%d
",n);
    n=Pop(ss,1);
    if(n>=0)
        printf("the pop num is:%d
",n);
    n=Pop(ss,1);
    if(n>=0)
        printf("the pop num is:%d
",n);
    n=Pop(ss,1);
    if(n>=0)
        printf("the pop num is:%d
",n);
    n=Pop(ss,1);
    if(n>=0)
        printf("the pop num is:%d
",n);
    n=Pop(ss,1);
    if(n>=0)
        printf("the pop num is:%d
",n);

    showStack(ss);

    return 0;
}

void createStack(shareStack * ss,int n,int m){
    int i;
    ss->top1 = -1;
    ss->top2 = MAXSIZE;
    for(i=0;i<n;i++){
        ss->top1++;
        ss->data[ss->top1] = 2*i+1;
    }
    for(i=0;i<m;i++){
        ss->top2--;
        ss->data[ss->top2] = 2*i+1;
    }
}

void showStack(shareStack *ss){
    int i;
    for(i=0;i<ss->top1+1;i++){
        printf("%d->",ss->data[i]);
    }
    printf("top1-----top2");
    for(i=ss->top2;i<MAXSIZE;i++){
        printf("<-%d",ss->data[i]);
    }
    printf("
");
}

int Push(shareStack *ss,int num,int flag){
    if(ss->top1+1 == ss->top2)
        return 0;
    if(flag == 1){
        ss->data[++ss->top1] = num;
        return 1;
    }else if( flag == 2){
        ss->data[--ss->top2] = num;
        return 1;
    }
    return 0;
}

int Pop(shareStack *ss,int flag){
    if(flag == 1){
        if(ss->top1 == -1)
            return -1;
        return ss->data[ss->top1--];
    }else if(flag == 2){
        if(ss->top2 == MAXSIZE)
            return -1;
        return ss->data[ss->top2++];
    }
    return -1;
}

运行结果