C++ 代码

#include <iostream>
using namespace std;

const int N = 100010;

int q[N],tail;

int main(){
    int n;
    cin >> n;
    while(n--){
        string op;
        int x;
        cin >> op ;
        if(op == "push"){
            cin >> x;
            q[++tail] = x;
        }else if(op == "pop"){
            --tail;
        }else if(op == "query"){
            cout << q[tail] <<endl;
        }else{
            if (tail == 0) cout << "YES" <<endl;
            else cout << "NO" <<endl;
        }
    }
    return 0;
}