题解 | 【模板】队列

#include <deque>
#include <iostream>
#include <ostream>
using namespace std;

int main() {
    int n ;
    cin>> n;
    deque<int> q;
    for(int i = 0 ; i < n; i++){
        string s ;
        cin>>s;
        //cout<<s<<"---";
        if(s[1]=='u'){
            int t ;
            cin>>t;
            q.push_back(t);
        }
        if(s[1]=='o'){
            if(q.empty()){
                cout<<"error"<<endl;
            }
            else{
               cout<<q.front()<<endl;
            q.pop_front(); 
            }
        }
        else if(s[0]=='f'){
            if(q.empty()){
                cout<<"error"<<endl;
            }
            else{
               cout<<q.front()<<endl; 
            }
        }
    }
    return 0;
}
// 64 位输出请用 printf("%lld")

stl