题目说的很明白了，按照题意做就行了

 

第一次用栈，wa了几次，注意弄清关系，别弄混当前页和栈中页的状态

 

就不多说了

 

#include<iostream>

#include<stack>

#include<string>

//#include<fstream>

using namespace std;

int main()

{

string p = "http://www.acm.org/";

stack<string> backward;

stack<string> forward;

string s;

backward.push(p);

//ifstream cin("in.txt");

while(cin>>s,s != "QUIT")

{

if(s == "VISIT")

{

cin>>s;

cout<<s<<endl;

backward.push(s);

while(!forward.empty())

forward.pop();

}

else if(s == "BACK")

{

// cout<<backward.size()<<endl;

if(backward.size() >= 2)

//if(!backward.empty())

{

forward.push(backward.top());

backward.pop();

cout<<backward.top()<<endl;

}

else

{

cout<<"Ignored"<<endl;

}

}

else if(s == "FORWARD")

{

if(!forward.empty())

{

cout<<forward.top()<<endl;

backward.push(forward.top());

forward.pop();

}

else

{

cout<<"Ignored"<<endl;

}

}

}

}