每日一题16：在一个数组中实现两个栈

在一个数组中实现两个栈，当数组未填满是任一个栈不能溢出。解法是将一个栈从头开始往后插入，而另一个从后往前插入，如果插入一个元素后，两个栈的top指针未相遇，则表示数组未满，栈没有溢出。

#include "stdafx.h"#include <iostream>using namespace std;struct special_stack{    int capcity;    int ltop,rtop;    int* vals;};special_stack* create(int capacity){    special_stack* sstack = new special_stack;    sstack->vals = new int[capacity];    sstack->capcity = capacity;    sstack->ltop = -1;    sstack->rtop = capacity;    return sstack;}bool lpush(special_stack** sstack,int val){    if((*sstack)->ltop + 1 == (*sstack)->rtop) return false;    (*sstack)->vals[++((*sstack)->ltop)] = val;    return true;}bool lpop(special_stack** sstack,int& val){    if((*sstack)->ltop < 0) return false;    val = (*sstack)->vals[((*sstack)->ltop)--];    return true;}bool rpush(special_stack** sstack,int val){    if((*sstack)->rtop - 1 == (*sstack)->ltop) return false;    (*sstack)->vals[--((*sstack)->rtop)] = val;    return true;}bool rpop(special_stack** sstack,int& val){    if((*sstack)->rtop >= (*sstack)->capcity) return false;    val = (*sstack)->vals[((*sstack)->rtop)++];    return true;}void destroy(special_stack** sstack){    delete [](*sstack)->vals;    delete (*sstack);    *sstack = NULL;}void clear(special_stack** sstack){    (*sstack)->ltop = -1;    (*sstack)->rtop = (*sstack)->capcity;}int _tmain(int argc, _TCHAR* argv[]){    special_stack* stack = create(20);    for (int i = 1; i <= 10; ++i)    {        lpush(&stack,i);        rpush(&stack,i + 10);    }    for (int i = 1; i <= 10; ++i)    {        int val;        if(lpop(&stack,val))            cout<<val<<' ';    }    cout<<endl;    for (int i = 1; i <= 10; ++i)    {        int val;        if(rpop(&stack,val))            cout<<val<<' ';    }    cout<<endl;    for (int i = 1; i <= 10; ++i)    {        lpush(&stack,i);        rpush(&stack,i + 10);    }    cout<<lpush(&stack,21)<<endl;    cout<<rpush(&stack,31)<<endl;    int val;    lpop(&stack,val);    rpop(&stack,val);    cout<<lpush(&stack,21)<<endl;    cout<<rpush(&stack,31)<<endl;    destroy(&stack);    return 0;}