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一、两栈共享

如果有两个相同类型的栈，为它们各自开辟数组空间，极有可能是一个栈已经满了，而另一个栈可能还是空闲。这时我们就可以用一个数组来存储两个栈。将数组的两端作为两个栈底，top1,top2两个栈顶向中间靠拢，当top1+1==top2时，栈空间满。

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

二、两栈共享的相关操作实现

1.初始化

/*共享栈的初始化*/
void InitStack(DoubleStack *stack)
{
    stack->top1=-1;
    stack->top2=MAXSIZE;
}

2.清空共享栈

/*清空栈*/
void ClearStack(DoubleStack *stack)
{
    stack->top1=-1;
    stack->top2=MAXSIZE;
}

3.求栈空间中总的元素的个数

/*求栈中元素的个数*/
int StackLength(DoubleStack stack)
{
    return (stack.top1+1)+(MAXSIZE-stack.top2);
}

3.指定栈并入栈

/*指定栈并入栈*/
int Push(DoubleStack *stack,ElementType e,int StackNumber)
{
    if(stack->top1+1==stack->top2)
    return 0;
    if(StackNumber==1)
    {
        stack->data[++stack->top1]=e;
    }else if(StackNumber==2)
    {
        stack->data[--stack->top2]=e;
    }
    return 1;
}

4.指定栈并出栈

/*指定栈并出栈*/
int Pop(DoubleStack *stack,ElementType *e,int StackNumber)
{
    if(StackNumber==1)
    {
        if(stack->top1==-1)
        return 0;

        *e=stack->data[stack->top1--];
    }
    else if(StackNumber==2)
    {
        if(stack->top2==MAXSIZE)
        return 0;

        *e=stack->data[stack->top2++];
    }
    return 1;
}

5.依次遍历栈空间中的元素

/*依次遍历并输出栈空间中的元素*/
void StackTraverse(DoubleStack stack)
{
    int i=0;
    while(i<=stack.top1)
    {
        printf("%d ",stack.data[i++]);
    }
    i=stack.top2;
    while(i<MAXSIZE)
    {
        printf("%d ",stack.data[i++]);
    }
    printf("\n");
}

三、具体代码实现

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

#define MAXSIZE 100

typedef int ElementType;

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

/*共享栈的初始化*/
void InitStack(DoubleStack *stack)
{
    stack->top1=-1;
    stack->top2=MAXSIZE;
}

/*清空栈*/
void ClearStack(DoubleStack *stack)
{
    stack->top1=-1;
    stack->top2=MAXSIZE;
}

/*求栈中元素的个数*/
int StackLength(DoubleStack stack)
{
    return (stack.top1+1)+(MAXSIZE-stack.top2);
}

/*指定栈并入栈*/
int Push(DoubleStack *stack,ElementType e,int StackNumber)
{
    if(stack->top1+1==stack->top2)
    return 0;
    if(StackNumber==1)
    {
        stack->data[++stack->top1]=e;
    }else if(StackNumber==2)
    {
        stack->data[--stack->top2]=e;
    }
    return 1;
}

/*指定栈并出栈*/
int Pop(DoubleStack *stack,ElementType *e,int StackNumber)
{
    if(StackNumber==1)
    {
        if(stack->top1==-1)
        return 0;

        *e=stack->data[stack->top1--];
    }
    else if(StackNumber==2)
    {
        if(stack->top2==MAXSIZE)
        return 0;

        *e=stack->data[stack->top2++];
    }
    return 1;
}

/*依次遍历并输出栈空间中的元素*/
void StackTraverse(DoubleStack stack)
{
    int i=0;
    while(i<=stack.top1)
    {
        printf("%d ",stack.data[i++]);
    }
    i=stack.top2;
    while(i<MAXSIZE)
    {
        printf("%d ",stack.data[i++]);
    }
    printf("\n");
}

/*样例测试*/
void StackTest()
{
    DoubleStack stack;
    int i;
    ElementType e;

    InitStack(&stack);
    for(i=1;i<7;i++)
    {
        Push(&stack,i,1);
    }
    for(i=MAXSIZE;i>=MAXSIZE-2;i--)
    {
        Push(&stack,i,2);
    }

    printf("There are %d elements in the stack.\n",StackLength(stack));
    printf("The elements in the stack are:\n");
    StackTraverse(stack);

    Pop(&stack,&e,2);
    printf("The element popped out of the stack is %d.\n",e);

    ClearStack(&stack);
    printf("After emptying the stack, the number of elements in the stack is %d.\n",StackLength(stack));

}

int main()
{
    StackTest();
    
    return 0;
}

四、样例输出

There are 9 elements in the stack

The elements in the stack are: 1 2 3 4 5 6 98 99 100

The element popped out of the stack is 98.

After emptying the stack, the number of elements in the stack is 0.

五、写在最后

这里是数据结构个人学习的笔记记录，如有问题欢迎指正说明。