ZOJ1061 Web Navigation

原始版本：

#include  < iostream >
#include  < stack >
#include  < string >
using   namespace  std;

void  ClearStack(stack < string >&  s)
{ // 清空栈
     while  ( ! s.empty())
    {
        s.pop();
    }
}
int  main( void )
{
     string  command,newURL;
     int  n,cases,i;
    cin >> n;
     for  (cases = 1 ;cases <= n; ++ cases)
    {
        stack < string >  forwardStack,backwardStack; // 前进栈，后退栈
         string  curURL  =   " http://www.acm.org/ " ; // 当前访问页面
         if  (cases != 1 )
        {
            cout << endl;
        }
         while (cin >> command)
        { // 读入一行命令
             if  (command[ 0 ] == ' Q ' )
            { // 退出
                 break ;
            }
             else   if (command[ 0 ] == ' B ' )
            { // 退后
                 if  ( ! backwardStack.empty())
                { // 退后栈中有历史记录
                    forwardStack.push(curURL); // 当前页面进入前进栈
                     // 从退出栈中栈顶取出页面为当前页面
                    curURL  =  backwardStack.top();
                    cout << curURL << endl;
                    backwardStack.pop();
                }
                 else
                {
                    cout << " Ignored " << endl;
                }
            }
             else   if (command[ 0 ] == ' V ' )
            { // 访问新URL
                backwardStack.push(curURL); // 当前页面进入后退栈
                cin >> curURL;
                cout << curURL << endl;
                ClearStack(forwardStack); // 情况前进栈
            }
             else   if (command[ 0 ] == ' F ' )
            { // 前进
                 if  ( ! forwardStack.empty())
                { // 前进栈中有历史记录
                    backwardStack.push(curURL); // 当前页面进入后退栈
                     // 从前进栈中栈顶取出页面为当前页面
                    curURL  =  forwardStack.top();
                    cout << curURL << endl;
                    forwardStack.pop();
                }
                 else
                {
                    cout << " Ignored " << endl;
                }
            }
        }
    }
     return   0 ;
}

重构后的版本：

#include  < iostream >
#include  < stack >
#include  < string >
using   namespace  std;

class  WebNavigation
{
private :
     string  curURL; // 当前访问页面
     string  command; // 当前待处理的命令
    stack < string >  forwardStack,backwardStack; // 前进栈，后退栈
     bool  isFinished; // 是否处理完毕

     void  ClearStack(stack < string >&  s); // 清空栈
     void  Back(); // 退后
     void  Forward(); // 向前
     void  Visit(); // 访问新URL
public :
    WebNavigation();
     ~ WebNavigation();
     bool  IsFinished() const
    { // 是否处理完毕
         return   this -> isFinished;
    }
     void  Process(); // 实际处理
    friend istream &   operator >>  (istream &   in ,WebNavigation &  webNavi);   
};

WebNavigation::WebNavigation()
{
     this -> curURL  =   " http://www.acm.org/ " ; // 默认首页
     this -> isFinished  =   false ;
}
WebNavigation:: ~ WebNavigation()
{ // 确保退出时清空使用的栈
    ClearStack( this -> forwardStack);
    ClearStack( this -> backwardStack);
}
void  WebNavigation::Back()
{ // 退后
     if  ( ! backwardStack.empty())
    { // 退后栈中有历史记录
        forwardStack.push(curURL); // 当前页面进入前进栈
         // 从退出栈中栈顶取出页面为当前页面
        curURL  =  backwardStack.top();
        cout << curURL << endl;
        backwardStack.pop();
    }
     else
    {
        cout << " Ignored " << endl;
    }
}
void  WebNavigation::ClearStack(stack < string >&  s)
{ // 清空栈
     while  ( ! s.empty())
    {
        s.pop();
    }
}
void  WebNavigation::Forward()
{ // 向前
     if  ( ! forwardStack.empty())
    { // 前进栈中有历史记录
        backwardStack.push(curURL); // 当前页面进入后退栈
         // 从前进栈中栈顶取出页面为当前页面
        curURL  =  forwardStack.top();
        cout << curURL << endl;
        forwardStack.pop();
    }
     else
    {
        cout << " Ignored " << endl;
    }
}
void  WebNavigation::Visit()
{ // 访问新URL
    backwardStack.push(curURL); // 当前页面进入后退栈
    cin >> curURL;
    cout << curURL << endl;
    ClearStack(forwardStack); // 清空前进栈
}
void  WebNavigation::Process()
{
     if  (command[ 0 ] == ' Q ' )
    { // 退出
         this -> isFinished  =   true ;
    }
     else   if (command[ 0 ] == ' B ' )
    { // 退后
         this -> Back();
    }
     else   if (command[ 0 ] == ' V ' )
    { // 访问新URL
         this -> Visit();
    }
     else   if (command[ 0 ] == ' F ' )
    { // 前进
         this -> Forward();
    }
}
istream &   operator >>  (istream &   in ,WebNavigation &  webNavi)
{ // 输入当前命令
     in >> webNavi.command;
     return   in ;
}

int  main( void )
{
     int  n,cases,i;
    cin >> n;
     for  (cases = 1 ;cases <= n; ++ cases)
    {
        WebNavigation webNavior;
         if  (cases != 1 )
        {
            cout << endl;
        }
         while (cin >> webNavior)
        { // 读入一行命令
            webNavior.Process();
             if  (webNavior.IsFinished())
            { // 已经处理完毕
                 break ;
            }
        }
    }
     return   0 ;
}