Poj 1028

传送门

模拟网页浏览，设置两个栈，一个往前一个往后，浏览新的网页时清空往前的栈

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

int main(){
    stack<string> webback,webforward;
    webback.push("http://www.acm.org/");
    string cmd,url;
    while(cin>>cmd){
        if(cmd[0]=='B'){//BACK
            if(webback.size()==1){
                cout<<"Ignored"<<endl;
            }
            else{
                webforward.push(webback.top());
                webback.pop();
                cout<<webback.top()<<endl;
            }
        }
        else if(cmd[0]=='F'){//FORWARD
            if(webforward.empty()){
                cout<<"Ignored"<<endl;
            }
            else{
                webback.push(webforward.top());
                webforward.pop();
                cout<<webback.top()<<endl;
            }
        }
        else if(cmd[0]=='V'){//VISIT
            cin>>url;
            while(!webforward.empty()){
                webforward.pop();
            }
            webback.push(url);
            cout<<webback.top()<<endl;
        }
        else if(cmd[0]=='Q'){//QUIT
            break;
        }
    }
}