1 #include<iostream> 2 #include<stack> 3 using namespace std; 4 class min_stack 5 { 6 public: 7     void push(int); 8     void  pop(); 9     int min();10     int size()11     {12         return data.size();13     }14 private:15     stack<int> data;16     stack<int> min_data;17 };18 void min_stack::push(int value)19 {20     data.push(value);21     if (min_data.size()==0 || min_data.top() > value)22     { 23         min_data.push(value);24     }25     else26     {27         min_data.push(min_data.top());28     }29 }30 void min_stack::pop()31 {32     if (data.size()>0)33     {34         min_data.pop();35         data.pop();36     }37 }38 int min_stack::min()39 {40     return min_data.top();41 }42  43 int main(int argc, char **argv)44 {45     int n,m;46     char ci;47     while(cin>>n)48     {49         min_stack mystack;50         for (int i=0; i<n; i++)51         {52             cin>>ci;53             switch (ci)54             {55             case ‘s‘:56                 cin>>m;57                 mystack.push(m);58                 cout<<mystack.min()<<endl;59                 break;60             case ‘o‘:61                 mystack.pop();62                 if (mystack.size()==0)63                 {64                     cout<<"NULL"<<endl;65                 }66                 else67                 {68                     cout<<mystack.min()<<endl;69                 }70                 break;71             }72         }   73     }74        return 1;75 }76 /**************************************************************77     Problem: 152278     User: xuebintian79     Language: C++80     Result: Accepted81     Time:140 ms82     Memory:1524 kb83 ****************************************************************/