ZOJ1061

题目链接：http://acm.zju.edu.cn/onlinejudge/showProblem.do?problemId=61

用容器stack，剩下的就是模拟了。

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

stack<string> Front; //前进栈
stack<string> Back;  //后退栈
string URL;  //当前页

void BACK(string order)
{
    if (Back.empty())
    {
        cout<<"Ignored"<<endl;
        return;
    }

    order = order.erase(0,4);
    Front.push(URL);
    URL = Back.top();
    Back.pop();
    cout<<URL<<endl;
}

void FORWARD(string order)
{
    if (Front.empty())
    {
        cout<<"Ignored"<<endl;
        return;
    }

    order = order.erase(0,7);
    Back.push(URL);
    URL = Front.top();
    Front.pop();
    cout<<URL<<endl;
}

void VISIT(string order)
{
    order = order.erase(0,6);
    Back.push(URL);
    URL = order;
    cout<<URL<<endl;
    while (!Front.empty()) Front.pop();
}

int main()
{
    int N;
    cin>>N;
    while (N--)
    {
        string order;
        bool Exit = false;
        URL = "http://www.acm.org/";
        while (getline(cin,order) && order!="QUIT")
        {
            switch (order[0])
            {
                case 'B':BACK(order);break;
                case 'F':FORWARD(order);break;
                case 'V':VISIT(order);break;
            }
        }
        while (!Front.empty()) Front.pop();
        while (!Back.empty()) Back.pop();
        if (N)
        {
            cin.ignore();
            cout<<endl;
        }
    }
    return 0;
}