题解

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

stack <int> q;

int main(){
    int n;
    cin >> n;
    for (int i=1; i<=n; i++){
        string s;
        cin >> s;
        if (s == "empty"){
            cout << (q.empty() ? "yes" : "no") << endl;
        }else if (s == "push"){
            int k;
            cin >> k;
            q.push(k);
        }else if (s == "pop"){
            if (q.empty()){
                cout << "pop fail" << endl;
            }else{
                cout << "pop " << q.top() << endl;
                q.pop();
            }
        }else if (s == "size"){
            cout << "size = " << q.size() << endl;
        }else if (s == "top"){
            if (q.empty()){
                cout << "top fail" << endl;
            }else{
                cout << "top = " << q.top() << endl;
            }
        }
    }
    return 0;
}